diff --git a/Backend/Auth.py b/Backend/Auth.py
index c4fca17..e2af48e 100644
--- a/Backend/Auth.py
+++ b/Backend/Auth.py
@@ -6,6 +6,7 @@ from typing import Any
 
 from fastapi import Depends, HTTPException, Request
 
+from Groups import AdminGroupName, GetGroupsForUser, IsUserInGroup
 from Users import GetUser
 
 
@@ -39,9 +40,14 @@ def GetCurrentUser(request: Request) -> dict[str, Any]:
     if User is None:
         raise HTTPException(status_code=401, detail="Session user no longer exists.")
 
+    # Admin isn't a stored flag — it's membership in the built-in Admin
+    # group, computed live, so it behaves exactly like any other group.
+    UserGroups = GetGroupsForUser(Username)
+
     return {
         "Username": Username,
-        "IsAdmin": User.get("IsAdmin", False),
+        "IsAdmin": AdminGroupName in UserGroups,
+        "Groups": UserGroups,
         "Colour": User.get("Colour", "Purple"),
     }
 
diff --git a/Backend/Blame.py b/Backend/Blame.py
index 475938b..399bd28 100644
--- a/Backend/Blame.py
+++ b/Backend/Blame.py
@@ -44,6 +44,33 @@ def SaveBlame(RootName: str, RelativePath: str, Blame: dict[str, dict[str, Any]]
         tomli_w.dump({"Lines": Blame}, BlameFile)
 
 
+def RenameUserInBlame(OldUsername: str, NewUsername: str) -> None:
+    """Rewrite every recorded blame attribution from OldUsername to
+    NewUsername across every file's blame history — called when a user
+    renames their account, so past attributions stay coherent.
+    """
+    BlameDirectory = GetBlameDirectory()
+
+    if not BlameDirectory.is_dir():
+        return
+
+    for BlamePath in BlameDirectory.rglob("*.blame.toml"):
+        with BlamePath.open("rb") as BlameFile:
+            Loaded = tomllib.load(BlameFile)
+
+        Lines = Loaded.get("Lines", {})
+        Changed = False
+
+        for Entry in Lines.values():
+            if Entry.get("Username") == OldUsername:
+                Entry["Username"] = NewUsername
+                Changed = True
+
+        if Changed:
+            with BlamePath.open("wb") as BlameFile:
+                tomli_w.dump({"Lines": Lines}, BlameFile)
+
+
 def UpdateBlameOnSave(
     RootName: str, RelativePath: str, OldContent: str, NewContent: str, Username: str
 ) -> None:
diff --git a/Backend/Groups.py b/Backend/Groups.py
new file mode 100644
index 0000000..26ffac8
--- /dev/null
+++ b/Backend/Groups.py
@@ -0,0 +1,140 @@
+from __future__ import annotations
+
+import tomllib
+
+from typing import Any
+
+import tomli_w
+
+from Settings import GetDataDirectory
+
+
+AdminGroupName = "Admin"
+
+
+def GetGroupsPath():
+    return GetDataDirectory() / "Groups.toml"
+
+
+def LoadGroups() -> dict[str, list[str]]:
+    GroupsPath = GetGroupsPath()
+
+    if not GroupsPath.is_file():
+        # First run after upgrading from the old boolean-flag admin model:
+        # seed the Admin group from whoever already had IsAdmin set, so
+        # nobody silently loses admin access.
+        from Users import LoadUsers
+
+        SeededAdmins = [
+            Username for Username, Data in LoadUsers().items() if Data.get("IsAdmin", False)
+        ]
+        Groups = {AdminGroupName: SeededAdmins}
+        SaveGroups(Groups)
+        return Groups
+
+    with GroupsPath.open("rb") as GroupsFile:
+        Loaded = tomllib.load(GroupsFile)
+
+    Groups = Loaded.get("Groups", {})
+
+    if AdminGroupName not in Groups:
+        Groups[AdminGroupName] = []
+        SaveGroups(Groups)
+
+    return Groups
+
+
+def SaveGroups(Groups: dict[str, list[str]]) -> None:
+    GetDataDirectory().mkdir(parents=True, exist_ok=True)
+
+    with GetGroupsPath().open("wb") as GroupsFile:
+        tomli_w.dump({"Groups": Groups}, GroupsFile)
+
+
+def ListGroups() -> list[dict[str, Any]]:
+    Groups = LoadGroups()
+    return [{"Name": Name, "Members": Members} for Name, Members in sorted(Groups.items())]
+
+
+def CreateGroup(Name: str) -> None:
+    Name = Name.strip()
+
+    if not Name:
+        raise ValueError("Group name cannot be empty.")
+
+    Groups = LoadGroups()
+
+    if Name in Groups:
+        raise ValueError(f"Group '{Name}' already exists.")
+
+    Groups[Name] = []
+    SaveGroups(Groups)
+
+
+def DeleteGroup(Name: str) -> None:
+    if Name == AdminGroupName:
+        raise ValueError("The Admin group can't be deleted.")
+
+    Groups = LoadGroups()
+
+    if Name not in Groups:
+        raise ValueError(f"Group '{Name}' does not exist.")
+
+    del Groups[Name]
+    SaveGroups(Groups)
+
+
+def SetGroupMembers(Name: str, Members: list[str]) -> None:
+    Groups = LoadGroups()
+
+    if Name not in Groups:
+        raise ValueError(f"Group '{Name}' does not exist.")
+
+    # De-duplicate while keeping things predictable.
+    Groups[Name] = sorted(set(Members))
+    SaveGroups(Groups)
+
+
+def AddMember(GroupName: str, Username: str) -> None:
+    Groups = LoadGroups()
+
+    if GroupName not in Groups:
+        raise ValueError(f"Group '{GroupName}' does not exist.")
+
+    if Username not in Groups[GroupName]:
+        Groups[GroupName].append(Username)
+        SaveGroups(Groups)
+
+
+def RemoveMember(GroupName: str, Username: str) -> None:
+    Groups = LoadGroups()
+
+    if GroupName not in Groups:
+        raise ValueError(f"Group '{GroupName}' does not exist.")
+
+    if Username in Groups[GroupName]:
+        Groups[GroupName].remove(Username)
+        SaveGroups(Groups)
+
+
+def GetGroupsForUser(Username: str) -> list[str]:
+    Groups = LoadGroups()
+    return [Name for Name, Members in Groups.items() if Username in Members]
+
+
+def IsUserInGroup(Username: str, GroupName: str) -> bool:
+    return Username in LoadGroups().get(GroupName, [])
+
+
+def RenameUserInGroups(OldUsername: str, NewUsername: str) -> None:
+    Groups = LoadGroups()
+    Changed = False
+
+    for Members in Groups.values():
+        if OldUsername in Members:
+            Members.remove(OldUsername)
+            Members.append(NewUsername)
+            Changed = True
+
+    if Changed:
+        SaveGroups(Groups)
diff --git a/Backend/Locks.py b/Backend/Locks.py
new file mode 100644
index 0000000..d44df00
--- /dev/null
+++ b/Backend/Locks.py
@@ -0,0 +1,124 @@
+from __future__ import annotations
+
+import tomllib
+
+from typing import Any
+
+import tomli_w
+from fastapi import HTTPException
+
+from Settings import GetDataDirectory
+
+
+def GetLocksPath():
+    return GetDataDirectory() / "LockedDirectories.toml"
+
+
+def LoadLocks() -> list[dict[str, Any]]:
+    LocksPath = GetLocksPath()
+
+    if not LocksPath.is_file():
+        return []
+
+    with LocksPath.open("rb") as LocksFile:
+        Loaded = tomllib.load(LocksFile)
+
+    return Loaded.get("Locks", [])
+
+
+def SaveLocks(Locks: list[dict[str, Any]]) -> None:
+    GetDataDirectory().mkdir(parents=True, exist_ok=True)
+
+    with GetLocksPath().open("wb") as LocksFile:
+        tomli_w.dump({"Locks": Locks}, LocksFile)
+
+
+def GetLockForPath(RootName: str, RelativePath: str) -> dict[str, Any] | None:
+    for Lock in LoadLocks():
+        if Lock.get("Root") == RootName and Lock.get("Path") == RelativePath:
+            return Lock
+
+    return None
+
+
+def SetLock(RootName: str, RelativePath: str, Usernames: list[str], GroupNames: list[str]) -> None:
+    """Restrict a file or directory to specific users and/or groups. Passing
+    both empty lists is the same as removing the lock entirely.
+    """
+    if not RelativePath:
+        raise ValueError("Can't lock an entire root — pick a specific file or directory.")
+
+    if not Usernames and not GroupNames:
+        RemoveLock(RootName, RelativePath)
+        return
+
+    Locks = LoadLocks()
+
+    for Lock in Locks:
+        if Lock.get("Root") == RootName and Lock.get("Path") == RelativePath:
+            Lock["Users"] = Usernames
+            Lock["Groups"] = GroupNames
+            SaveLocks(Locks)
+            return
+
+    Locks.append({"Root": RootName, "Path": RelativePath, "Users": Usernames, "Groups": GroupNames})
+    SaveLocks(Locks)
+
+
+def RemoveLock(RootName: str, RelativePath: str) -> None:
+    Locks = [
+        Lock
+        for Lock in LoadLocks()
+        if not (Lock.get("Root") == RootName and Lock.get("Path") == RelativePath)
+    ]
+    SaveLocks(Locks)
+
+
+def IsPathAccessible(
+    RootName: str, RelativePath: str, Username: str, UserGroups: list[str], IsAdmin: bool
+) -> bool:
+    """A path is inaccessible if it IS a locked file/directory, or lies
+    anywhere underneath a locked directory, and the user isn't permitted
+    (by username or group) on every applicable lock. Locks don't propagate
+    to subdirectories as separate records — there's only ever one lock
+    entry per locked directory — but access to anything inside still
+    requires being permitted on that ancestor lock, so you always have to
+    "enter the parent first." Admins bypass every lock.
+    """
+    if IsAdmin:
+        return True
+
+    for Lock in LoadLocks():
+        if Lock.get("Root") != RootName:
+            continue
+
+        LockPath = Lock.get("Path", "")
+
+        if not LockPath:
+            continue
+
+        if RelativePath == LockPath or RelativePath.startswith(f"{LockPath}/"):
+            PermittedUsers = Lock.get("Users", [])
+            PermittedGroups = Lock.get("Groups", [])
+            IsPermittedByUser = Username in PermittedUsers
+            IsPermittedByGroup = any(Group in PermittedGroups for Group in UserGroups)
+
+            if not IsPermittedByUser and not IsPermittedByGroup:
+                return False
+
+    return True
+
+
+def RequirePathAccessible(RootName: str, RelativePath: str, CurrentUser: dict[str, Any]) -> None:
+    """Raises a 404 (never a distinguishing "access denied") for a path the
+    current user isn't permitted to see, so a locked directory's existence
+    isn't revealed to anyone not on its list.
+    """
+    if not IsPathAccessible(
+        RootName,
+        RelativePath,
+        CurrentUser["Username"],
+        CurrentUser.get("Groups", []),
+        CurrentUser.get("IsAdmin", False),
+    ):
+        raise HTTPException(status_code=404, detail="Not found.")
diff --git a/Backend/Main.py b/Backend/Main.py
index f788fa4..647779a 100644
--- a/Backend/Main.py
+++ b/Backend/Main.py
@@ -15,10 +15,25 @@ from fastapi.staticfiles import StaticFiles
 
 from Auth import CreateSession, DeleteSession, GetCurrentUser, RequireAdmin, SessionCookieName
 from BookReader import ReadBookForFile
-from Blame import LoadBlame, UpdateBlameOnSave
+from Blame import LoadBlame, RenameUserInBlame, UpdateBlameOnSave
 from Core import ResolvePath
 from Editor import WriteTextFile
 from Explorer import ClassifyFile, CreateEntry, DeleteEntry, ListDirectory, ListRoots, MoveEntry
+from Groups import (
+    CreateGroup,
+    DeleteGroup,
+    ListGroups,
+    RenameUserInGroups,
+    SetGroupMembers,
+)
+from Locks import (
+    GetLockForPath,
+    IsPathAccessible,
+    LoadLocks,
+    RemoveLock,
+    RequirePathAccessible,
+    SetLock,
+)
 from Preview import GetFileSize, GetMimeType, ParseRangeHeader, ReadTextFile, TextFileTypes
 from Settings import (
     DeleteTheme,
@@ -26,18 +41,22 @@ from Settings import (
     LoadSettings,
     LoadTheme,
     PaletteRoles,
+    RenameUserSettings,
     SaveSettings,
     SaveTheme,
 )
 from Users import (
     AnyUsersExist,
+    ChangePassword,
     CreateUser,
     GetAvatarPath,
     ListUsers,
+    RenameUser,
+    RenameUserAvatar,
+    SaveAvatar,
     UpdateUserColour,
     UserColourOptions,
     VerifyLogin,
-    SaveAvatar,
 )
 from pydantic import BaseModel
 
@@ -122,7 +141,7 @@ class CreateUserRequest(BaseModel):
 
 
 @Application.get("/api/users")
-def GetUsersEndpoint(CurrentUser: dict = Depends(RequireAdmin)) -> list[dict]:
+def GetUsersEndpoint(CurrentUser: dict = Depends(GetCurrentUser)) -> list[dict]:
     return ListUsers()
 
 
@@ -136,7 +155,7 @@ def PostUsersEndpoint(Body: CreateUserRequest, CurrentUser: dict = Depends(Requi
     return {"Created": True}
 
 
-# --- Profile (colour + avatar) --------------------------------------------
+# --- Profile (colour, avatar, username, password) --------------------------
 
 
 @Application.get("/api/profile/colours")
@@ -186,6 +205,163 @@ def GetProfileAvatarEndpoint(Username: str, CurrentUser: dict = Depends(GetCurre
     return StreamingResponse(iter([AvatarPath.read_bytes()]), media_type=MimeType)
 
 
+class ChangeUsernameRequest(BaseModel):
+    NewUsername: str
+
+
+@Application.put("/api/profile/username")
+def PutProfileUsernameEndpoint(
+    Body: ChangeUsernameRequest,
+    request: Request,
+    response: Response,
+    CurrentUser: dict = Depends(GetCurrentUser),
+) -> dict:
+    OldUsername = CurrentUser["Username"]
+    NewUsername = Body.NewUsername.strip()
+
+    try:
+        RenameUser(OldUsername, NewUsername)
+    except ValueError as Error:
+        raise HTTPException(status_code=400, detail=str(Error))
+
+    if NewUsername != OldUsername:
+        RenameUserSettings(OldUsername, NewUsername)
+        RenameUserAvatar(OldUsername, NewUsername)
+        RenameUserInBlame(OldUsername, NewUsername)
+        RenameUserInGroups(OldUsername, NewUsername)
+
+        # Re-authenticate this same request under the new name so the
+        # person doesn't get logged out by their own rename. Any OTHER
+        # active session for the old name is left to fail naturally on its
+        # next request — a re-login there is the simplest correct outcome.
+        OldToken = request.cookies.get(SessionCookieName)
+        if OldToken:
+            DeleteSession(OldToken)
+
+        NewToken = CreateSession(NewUsername)
+        response.set_cookie(
+            key=SessionCookieName,
+            value=NewToken,
+            httponly=True,
+            samesite="lax",
+            max_age=60 * 60 * 24 * 30,
+        )
+
+    return {"Username": NewUsername, "IsAdmin": CurrentUser["IsAdmin"], "Colour": CurrentUser["Colour"]}
+
+
+class ChangePasswordRequest(BaseModel):
+    CurrentPassword: str
+    NewPassword: str
+
+
+@Application.put("/api/profile/password")
+def PutProfilePasswordEndpoint(
+    Body: ChangePasswordRequest, CurrentUser: dict = Depends(GetCurrentUser)
+) -> dict:
+    try:
+        ChangePassword(CurrentUser["Username"], Body.CurrentPassword, Body.NewPassword)
+    except ValueError as Error:
+        raise HTTPException(status_code=400, detail=str(Error))
+
+    return {"Changed": True}
+
+
+# --- Groups -----------------------------------------------------------------
+
+
+@Application.get("/api/groups")
+def GetGroupsEndpoint(CurrentUser: dict = Depends(GetCurrentUser)) -> list[dict]:
+    # Readable by anyone — picking an existing group as a lock target is
+    # open to everyone, same as picking a user.
+    return ListGroups()
+
+
+class CreateGroupRequest(BaseModel):
+    Name: str
+
+
+@Application.post("/api/groups")
+def PostGroupsEndpoint(Body: CreateGroupRequest, CurrentUser: dict = Depends(RequireAdmin)) -> dict:
+    try:
+        CreateGroup(Body.Name)
+    except ValueError as Error:
+        raise HTTPException(status_code=400, detail=str(Error))
+
+    return {"Created": True}
+
+
+@Application.delete("/api/groups")
+def DeleteGroupsEndpoint(Name: str, CurrentUser: dict = Depends(RequireAdmin)) -> dict:
+    try:
+        DeleteGroup(Name)
+    except ValueError as Error:
+        raise HTTPException(status_code=400, detail=str(Error))
+
+    return {"Deleted": True}
+
+
+class SetGroupMembersRequest(BaseModel):
+    Members: list[str]
+
+
+@Application.put("/api/groups/members")
+def PutGroupMembersEndpoint(
+    Name: str, Body: SetGroupMembersRequest, CurrentUser: dict = Depends(RequireAdmin)
+) -> dict:
+    try:
+        SetGroupMembers(Name, Body.Members)
+    except ValueError as Error:
+        raise HTTPException(status_code=400, detail=str(Error))
+
+    return {"Saved": True}
+
+
+# --- Locked files/directories -----------------------------------------------
+# Setting a lock is open to anyone who currently has access to the path —
+# not admin-only. If you can see it, you're trusted to decide who else can.
+# Admins additionally bypass every lock (see Locks.IsPathAccessible).
+
+
+@Application.get("/api/lock")
+def GetLockEndpoint(Root: str, Path: str, CurrentUser: dict = Depends(GetCurrentUser)) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+    return GetLockForPath(Root, Path) or {}
+
+
+class SetLockRequest(BaseModel):
+    Users: list[str] = []
+    Groups: list[str] = []
+
+
+@Application.put("/api/lock")
+def PutLockEndpoint(
+    Root: str, Path: str, Body: SetLockRequest, CurrentUser: dict = Depends(GetCurrentUser)
+) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+
+    try:
+        SetLock(Root, Path, Body.Users, Body.Groups)
+    except ValueError as Error:
+        raise HTTPException(status_code=400, detail=str(Error))
+
+    return {"Locked": True}
+
+
+@Application.delete("/api/lock")
+def DeleteLockEndpoint(Root: str, Path: str, CurrentUser: dict = Depends(GetCurrentUser)) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+    RemoveLock(Root, Path)
+    return {"Unlocked": True}
+
+
+@Application.get("/api/locks")
+def GetLocksEndpoint(CurrentUser: dict = Depends(RequireAdmin)) -> list[dict]:
+    # The full list (across every root/path) stays admin-only — it's a
+    # global overview, not a per-item action.
+    return LoadLocks()
+
+
 # --- Files ----------------------------------------------------------------
 
 
@@ -198,12 +374,32 @@ def GetRootsEndpoint(CurrentUser: dict = Depends(GetCurrentUser)) -> list[dict]:
 def GetTreeEndpoint(
     Root: str, Path: str = "", CurrentUser: dict = Depends(GetCurrentUser)
 ) -> list[dict]:
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     try:
         ShowHidden = LoadSettings(CurrentUser["Username"]).get("ShowHiddenFolders", False)
-        return ListDirectory(Root, Path, ShowHidden)
+        Entries = ListDirectory(Root, Path, ShowHidden)
     except (ValueError, NotADirectoryError, FileNotFoundError) as Error:
         raise HTTPException(status_code=400, detail=str(Error))
 
+    Username = CurrentUser["Username"]
+    UserGroups = CurrentUser.get("Groups", [])
+    IsAdmin = CurrentUser.get("IsAdmin", False)
+
+    # A locked subdirectory (or anything inside one) shouldn't even appear
+    # in its parent's listing for someone without access to it.
+    return [
+        Entry
+        for Entry in Entries
+        if IsPathAccessible(
+            Root,
+            f"{Path}/{Entry['Name']}" if Path else Entry["Name"],
+            Username,
+            UserGroups,
+            IsAdmin,
+        )
+    ]
+
 
 class CreateEntryRequest(BaseModel):
     IsDirectory: bool
@@ -213,6 +409,8 @@ class CreateEntryRequest(BaseModel):
 def PostTreeEndpoint(
     Root: str, Path: str, Body: CreateEntryRequest, CurrentUser: dict = Depends(GetCurrentUser)
 ) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     try:
         CreateEntry(Root, Path, Body.IsDirectory)
     except ValueError as Error:
@@ -234,6 +432,8 @@ class MoveEntryRequest(BaseModel):
 def PatchTreeEndpoint(
     Root: str, Path: str, Body: MoveEntryRequest, CurrentUser: dict = Depends(GetCurrentUser)
 ) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     if Body.DestinationPath:
         Destination = Body.DestinationPath
     elif Body.NewName:
@@ -242,6 +442,8 @@ def PatchTreeEndpoint(
     else:
         raise HTTPException(status_code=400, detail="Provide NewName or DestinationPath.")
 
+    RequirePathAccessible(Root, Destination, CurrentUser)
+
     try:
         MoveEntry(Root, Path, Destination)
     except ValueError as Error:
@@ -258,6 +460,8 @@ def PatchTreeEndpoint(
 
 @Application.delete("/api/tree")
 def DeleteTreeEndpoint(Root: str, Path: str, CurrentUser: dict = Depends(GetCurrentUser)) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     try:
         DeleteEntry(Root, Path)
     except ValueError as Error:
@@ -274,6 +478,8 @@ def DeleteTreeEndpoint(Root: str, Path: str, CurrentUser: dict = Depends(GetCurr
 def GetFileEndpoint(
     Root: str, Path: str, request: Request, CurrentUser: dict = Depends(GetCurrentUser)
 ):
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     try:
         FilePath = ResolvePath(Root, Path)
     except ValueError as Error:
@@ -322,6 +528,8 @@ def GetFileEndpoint(
 async def PutFileEndpoint(
     Root: str, Path: str, request: Request, CurrentUser: dict = Depends(GetCurrentUser)
 ):
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     try:
         FilePath = ResolvePath(Root, Path)
     except ValueError as Error:
@@ -348,12 +556,41 @@ async def PutFileEndpoint(
 
 @Application.get("/api/blame")
 def GetBlameEndpoint(Root: str, Path: str, CurrentUser: dict = Depends(GetCurrentUser)) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     try:
         ResolvePath(Root, Path)
     except ValueError as Error:
         raise HTTPException(status_code=400, detail=str(Error))
 
-    return LoadBlame(Root, Path)
+    RawBlame = LoadBlame(Root, Path)
+    AllUsers = {User["Username"]: User for User in ListUsers()}
+    ViewerUsername = CurrentUser["Username"]
+    Enriched: dict[str, dict] = {}
+
+    for LineNumber, Entry in RawBlame.items():
+        AuthorUsername = Entry.get("Username")
+        Timestamp = Entry.get("Timestamp")
+
+        if AuthorUsername == ViewerUsername:
+            IsVisible = True
+        elif AuthorUsername in AllUsers:
+            IsVisible = LoadSettings(AuthorUsername).get("VisibleInBlame", True)
+        else:
+            IsVisible = True
+
+        if IsVisible:
+            AuthorRecord = AllUsers.get(AuthorUsername, {})
+            Enriched[LineNumber] = {
+                "Username": AuthorUsername,
+                "Timestamp": Timestamp,
+                "Colour": AuthorRecord.get("Colour", "Purple"),
+                "HasAvatar": AuthorUsername is not None and GetAvatarPath(AuthorUsername) is not None,
+            }
+        else:
+            Enriched[LineNumber] = {"Username": None, "Hidden": True, "Timestamp": Timestamp}
+
+    return Enriched
 
 
 @Application.get("/api/raw/{RootName}/{FilePath:path}")
@@ -365,6 +602,8 @@ def GetRawFileEndpoint(
     and scripts INSIDE a previewed HTML document resolve correctly against
     sibling files in the same directory.
     """
+    RequirePathAccessible(RootName, FilePath, CurrentUser)
+
     try:
         ResolvedPath = ResolvePath(RootName, FilePath)
     except ValueError as Error:
@@ -385,6 +624,8 @@ def GetRawFileEndpoint(
 
 @Application.get("/api/book")
 def GetBookEndpoint(Root: str, Path: str, CurrentUser: dict = Depends(GetCurrentUser)) -> dict:
+    RequirePathAccessible(Root, Path, CurrentUser)
+
     try:
         FilePath = ResolvePath(Root, Path)
     except ValueError as Error:
diff --git a/Backend/Settings.py b/Backend/Settings.py
index b67794a..0bd15c5 100644
--- a/Backend/Settings.py
+++ b/Backend/Settings.py
@@ -42,6 +42,8 @@ DefaultSettings: dict[str, Any] = {
     "NewEntryButtonsAtTop": False,
     "StickyToolbar": True,
     "ConfirmBeforeDelete": True,
+    "VisibleInBlame": True,
+    "ShowBlameAvatars": False,
 }
 
 DefaultThemesDirectory = ApplicationDirectory / "DefaultThemes"
@@ -135,6 +137,13 @@ def SaveSettings(Username: str, NewSettings: dict[str, Any]) -> dict[str, Any]:
     return Merged
 
 
+def RenameUserSettings(OldUsername: str, NewUsername: str) -> None:
+    OldPath = GetSettingsPath(OldUsername)
+
+    if OldPath.is_file():
+        OldPath.rename(GetSettingsPath(NewUsername))
+
+
 def ListThemeNames() -> list[str]:
     EnsureDataDirectory()
     return sorted(ThemeFile.stem for ThemeFile in GetThemesDirectory().glob("*.toml"))
diff --git a/Backend/Users.py b/Backend/Users.py
index 231d61b..af427e3 100644
--- a/Backend/Users.py
+++ b/Backend/Users.py
@@ -12,6 +12,7 @@ import tomli_w
 
 from Settings import GetDataDirectory
 
+from Groups import AddMember, AdminGroupName, GetGroupsForUser
 
 Pbkdf2Iterations = 260_000
 
@@ -96,11 +97,13 @@ def CreateUser(Username: str, Password: str, IsAdmin: bool, Colour: str = Defaul
 
     Users[Username] = {
         "PasswordHash": HashPassword(Password),
-        "IsAdmin": IsAdmin,
         "Colour": Colour,
     }
     SaveUsers(Users)
 
+    if IsAdmin:
+        AddMember(AdminGroupName, Username)
+
 
 def UpdateUserColour(Username: str, Colour: str) -> None:
     if Colour not in UserColourOptions:
@@ -115,6 +118,44 @@ def UpdateUserColour(Username: str, Colour: str) -> None:
     SaveUsers(Users)
 
 
+def RenameUser(OldUsername: str, NewUsername: str) -> None:
+    NewUsername = NewUsername.strip()
+
+    if not NewUsername:
+        raise ValueError("Username cannot be empty.")
+
+    if NewUsername == OldUsername:
+        return
+
+    Users = LoadUsers()
+
+    if OldUsername not in Users:
+        raise ValueError("User not found.")
+
+    if NewUsername in Users:
+        raise ValueError(f"User '{NewUsername}' already exists.")
+
+    Users[NewUsername] = Users.pop(OldUsername)
+    SaveUsers(Users)
+
+
+def ChangePassword(Username: str, CurrentPassword: str, NewPassword: str) -> None:
+    User = GetUser(Username)
+
+    if User is None:
+        raise ValueError("User not found.")
+
+    if not VerifyPassword(CurrentPassword, User["PasswordHash"]):
+        raise ValueError("Current password is incorrect.")
+
+    if not NewPassword:
+        raise ValueError("New password cannot be empty.")
+
+    Users = LoadUsers()
+    Users[Username]["PasswordHash"] = HashPassword(NewPassword)
+    SaveUsers(Users)
+
+
 def VerifyLogin(Username: str, Password: str) -> dict[str, Any] | None:
     User = GetUser(Username)
 
@@ -126,7 +167,7 @@ def VerifyLogin(Username: str, Password: str) -> dict[str, Any] | None:
 
     return {
         "Username": Username,
-        "IsAdmin": User.get("IsAdmin", False),
+        "IsAdmin": AdminGroupName in GetGroupsForUser(Username),
         "Colour": User.get("Colour", DefaultUserColour),
     }
 
@@ -136,7 +177,7 @@ def ListUsers() -> list[dict[str, Any]]:
     return [
         {
             "Username": Name,
-            "IsAdmin": Data.get("IsAdmin", False),
+            "IsAdmin": AdminGroupName in GetGroupsForUser(Name),
             "Colour": Data.get("Colour", DefaultUserColour),
         }
         for Name, Data in Users.items()
@@ -168,3 +209,13 @@ def GetAvatarPath(Username: str) -> Path | None:
 
     Matches = sorted(Directory.glob(f"{Username}.*"))
     return Matches[0] if Matches else None
+
+
+def RenameUserAvatar(OldUsername: str, NewUsername: str) -> None:
+    Directory = GetAvatarDirectory()
+
+    if not Directory.is_dir():
+        return
+
+    for ExistingPath in Directory.glob(f"{OldUsername}.*"):
+        ExistingPath.rename(Directory / f"{NewUsername}{ExistingPath.suffix}")
diff --git a/Frontend/src/Api.js b/Frontend/src/Api.js
index 3ceb3c8..ae82629 100644
--- a/Frontend/src/Api.js
+++ b/Frontend/src/Api.js
@@ -81,6 +81,58 @@ export function GetAvatarUrl(Username) {
   return `${ApiBase}/profile/avatar?${Params}`;
 }
 
+export function UpdateUsername(NewUsername) {
+  return FetchJson("/profile/username", { method: "PUT", ...JsonBody({ NewUsername }) });
+}
+
+export function ChangePassword(CurrentPassword, NewPassword) {
+  return FetchJson("/profile/password", {
+    method: "PUT",
+    ...JsonBody({ CurrentPassword, NewPassword }),
+  });
+}
+
+// --- Groups ---------------------------------------------------------------
+
+export function FetchGroups() {
+  return FetchJson("/groups");
+}
+
+export function CreateGroupApi(Name) {
+  return FetchJson("/groups", { method: "POST", ...JsonBody({ Name }) });
+}
+
+export function DeleteGroupApi(Name) {
+  const Params = new URLSearchParams({ Name });
+  return FetchJson(`/groups?${Params}`, { method: "DELETE" });
+}
+
+export function SetGroupMembersApi(Name, Members) {
+  const Params = new URLSearchParams({ Name });
+  return FetchJson(`/groups/members?${Params}`, { method: "PUT", ...JsonBody({ Members }) });
+}
+
+// --- Locked files/directories -----------------------------------------
+
+export function FetchLocks() {
+  return FetchJson("/locks");
+}
+
+export function FetchLock(RootName, RelativePath) {
+  const Params = new URLSearchParams({ Root: RootName, Path: RelativePath });
+  return FetchJson(`/lock?${Params}`);
+}
+
+export function SetLock(RootName, RelativePath, Users, Groups) {
+  const Params = new URLSearchParams({ Root: RootName, Path: RelativePath });
+  return FetchJson(`/lock?${Params}`, { method: "PUT", ...JsonBody({ Users, Groups }) });
+}
+
+export function RemoveLock(RootName, RelativePath) {
+  const Params = new URLSearchParams({ Root: RootName, Path: RelativePath });
+  return FetchJson(`/lock?${Params}`, { method: "DELETE" });
+}
+
 // --- Files --------------------------------------------------------------
 
 export function FetchRoots() {
diff --git a/Frontend/src/App.jsx b/Frontend/src/App.jsx
index e8c5a1e..0ac93f8 100644
--- a/Frontend/src/App.jsx
+++ b/Frontend/src/App.jsx
@@ -238,6 +238,7 @@ export default function App() {
               FileType={ViewFileType}
               OnNavigateLink={HandleSelectFile}
               ShowGitBlame={Settings ? Settings.ShowGitBlame : false}
+              ShowBlameAvatars={Settings ? Settings.ShowBlameAvatars : false}
               StickyToolbar={Settings ? Settings.StickyToolbar : true}
             />
           )}
diff --git a/Frontend/src/Components/AccessModal.jsx b/Frontend/src/Components/AccessModal.jsx
new file mode 100644
index 0000000..a10f7ac
--- /dev/null
+++ b/Frontend/src/Components/AccessModal.jsx
@@ -0,0 +1,72 @@
+import React, { useState } from "react";
+
+import AccessPicker from "./AccessPicker.jsx";
+
+export default function AccessModal({
+  Title,
+  ShowNameField,
+  InitialName,
+  NamePlaceholder,
+  InitialUsers,
+  InitialGroups,
+  ConfirmLabel,
+  OnConfirm,
+  OnCancel,
+}) {
+  const [Name, SetName] = useState(InitialName || "");
+  const [Users, SetUsers] = useState(InitialUsers || []);
+  const [Groups, SetGroups] = useState(InitialGroups || []);
+
+  function HandleConfirm() {
+    OnConfirm(Name, Users, Groups);
+  }
+
+  function HandleRemoveRestriction() {
+    OnConfirm(Name, [], []);
+  }
+
+  const HasRestriction = (InitialUsers && InitialUsers.length > 0) || (InitialGroups && InitialGroups.length > 0);
+
+  return (
+    <div className="SettingsOverlay" onClick={OnCancel}>
+      <div className="SettingsModal" onClick={(Event) => Event.stopPropagation()}>
+        <div className="SettingsHeader">
+          <span>{Title}</span>
+          <button className="SettingsClose" onClick={OnCancel}>
+            ✕
+          </button>
+        </div>
+        <div className="SettingsBody">
+          {ShowNameField && (
+            <div className="SettingsRow">
+              <label className="SettingsLabel">Name</label>
+              <input
+                type="text"
+                value={Name}
+                onChange={(Event) => SetName(Event.target.value)}
+                placeholder={NamePlaceholder}
+                autoFocus
+              />
+            </div>
+          )}
+          <div className="SettingsRow">
+            <label className="SettingsLabel">Restrict access to (leave empty for everyone)</label>
+            <AccessPicker
+              SelectedUsers={Users}
+              SelectedGroups={Groups}
+              OnChangeUsers={SetUsers}
+              OnChangeGroups={SetGroups}
+            />
+          </div>
+        </div>
+        <div className="SettingsFooter">
+          {!ShowNameField && HasRestriction && (
+            <button onClick={HandleRemoveRestriction}>Remove restriction</button>
+          )}
+          <button onClick={OnCancel}>Cancel</button>
+          <button onClick={HandleConfirm}>{ConfirmLabel}</button>
+        </div>
+      </div>
+    </div>
+  );
+}
diff --git a/Frontend/src/Components/AccessPicker.jsx b/Frontend/src/Components/AccessPicker.jsx
new file mode 100644
index 0000000..84e51af
--- /dev/null
+++ b/Frontend/src/Components/AccessPicker.jsx
@@ -0,0 +1,75 @@
+import React, { useEffect, useState } from "react";
+
+import { FetchGroups, FetchUsers } from "../Api.js";
+
+export default function AccessPicker({ SelectedUsers, SelectedGroups, OnChangeUsers, OnChangeGroups }) {
+  const [AllUsers, SetAllUsers] = useState([]);
+  const [AllGroups, SetAllGroups] = useState([]);
+  const [Query, SetQuery] = useState("");
+
+  useEffect(() => {
+    FetchUsers().then(SetAllUsers);
+    FetchGroups().then(SetAllGroups);
+  }, []);
+
+  function ToggleUser(Username) {
+    if (SelectedUsers.includes(Username)) {
+      OnChangeUsers(SelectedUsers.filter((U) => U !== Username));
+    } else {
+      OnChangeUsers([...SelectedUsers, Username]);
+    }
+  }
+
+  function ToggleGroup(Name) {
+    if (SelectedGroups.includes(Name)) {
+      OnChangeGroups(SelectedGroups.filter((G) => G !== Name));
+    } else {
+      OnChangeGroups([...SelectedGroups, Name]);
+    }
+  }
+
+  const LowerQuery = Query.toLowerCase();
+  const FilteredGroups = AllGroups.filter((Group) => Group.Name.toLowerCase().includes(LowerQuery));
+  const FilteredUsers = AllUsers.filter((User) => User.Username.toLowerCase().includes(LowerQuery));
+
+  return (
+    <div className="AccessPicker">
+      <input
+        type="text"
+        placeholder="Search users or groups…"
+        value={Query}
+        onChange={(Event) => SetQuery(Event.target.value)}
+      />
+      <div className="AccessPickerList">
+        {FilteredGroups.map((Group) => (
+          <label className="AccessPickerRow" key={`group:${Group.Name}`}>
+            <input
+              type="checkbox"
+              checked={SelectedGroups.includes(Group.Name)}
+              onChange={() => ToggleGroup(Group.Name)}
+            />
+            <span className="AccessPickerType">Group</span>
+            <span>{Group.Name}</span>
+          </label>
+        ))}
+        {FilteredUsers.map((User) => (
+          <label className="AccessPickerRow" key={`user:${User.Username}`}>
+            <input
+              type="checkbox"
+              checked={SelectedUsers.includes(User.Username)}
+              onChange={() => ToggleUser(User.Username)}
+            />
+            <span
+              className="ColourSwatchSmall"
+              style={{ background: `var(--${User.Colour || "Purple"})` }}
+            />
+            <span>{User.Username}</span>
+          </label>
+        ))}
+        {FilteredGroups.length === 0 && FilteredUsers.length === 0 && (
+          <div className="AccessPickerEmpty">No matches.</div>
+        )}
+      </div>
+    </div>
+  );
+}
diff --git a/Frontend/src/Components/DirectoryPane.jsx b/Frontend/src/Components/DirectoryPane.jsx
index 3b2779c..56c993c 100644
--- a/Frontend/src/Components/DirectoryPane.jsx
+++ b/Frontend/src/Components/DirectoryPane.jsx
@@ -1,7 +1,16 @@
 import React, { useEffect, useState } from "react";
 
-import { CreateEntry, DeleteEntry, FetchTree, MoveEntry, RenameEntry } from "../Api.js";
+import {
+  CreateEntry,
+  DeleteEntry,
+  FetchLock,
+  FetchTree,
+  MoveEntry,
+  RenameEntry,
+  SetLock as SetLockApi,
+} from "../Api.js";
 import { GetFileIcon, GetFolderIcon } from "../IconStyle.js";
+import AccessModal from "./AccessModal.jsx";
 
 export default function DirectoryPane({
   RootName,
@@ -16,6 +25,7 @@ export default function DirectoryPane({
 }) {
   const [Entries, SetEntries] = useState([]);
   const [LoadError, SetLoadError] = useState(null);
+  const [ModalConfig, SetModalConfig] = useState(null);
 
   async function Reload() {
     try {
@@ -38,29 +48,29 @@ export default function DirectoryPane({
     return DirectoryPath ? `${DirectoryPath}/${Name}` : Name;
   }
 
-  async function HandleCreateFile() {
-    const Name = window.prompt("New file name (e.g. Notes.md):");
-    if (!Name) return;
-
-    try {
-      await CreateEntry(RootName, JoinPath(Name), false);
-      await Reload();
-      OnEntryCreated();
-    } catch (Error) {
-      SetLoadError(Error.message);
-    }
+  function OpenCreateFileModal() {
+    SetModalConfig({ Mode: "createFile" });
   }
 
-  async function HandleCreateDirectory() {
-    const Name = window.prompt("New directory name:");
-    if (!Name) return;
+  function OpenCreateDirectoryModal() {
+    SetModalConfig({ Mode: "createDirectory" });
+  }
+
+  async function HandleRequestLockEdit(Event, Entry) {
+    Event.stopPropagation();
+    const FullPath = JoinPath(Entry.Name);
 
     try {
-      await CreateEntry(RootName, JoinPath(Name), true);
-      await Reload();
-      OnEntryCreated();
+      const Existing = await FetchLock(RootName, FullPath);
+      SetModalConfig({
+        Mode: "editLock",
+        TargetPath: FullPath,
+        EntryName: Entry.Name,
+        InitialUsers: (Existing && Existing.Users) || [],
+        InitialGroups: (Existing && Existing.Groups) || [],
+      });
     } catch (Error) {
-      SetLoadError(Error.message);
+      window.alert(Error.message);
     }
   }
 
@@ -101,11 +111,37 @@ export default function DirectoryPane({
     }
   }
 
+  async function HandleModalConfirm(Name, Users, Groups) {
+    try {
+      if (ModalConfig.Mode === "createFile" || ModalConfig.Mode === "createDirectory") {
+        if (!Name || !Name.trim()) return;
+
+        const IsDirectory = ModalConfig.Mode === "createDirectory";
+        const FullPath = JoinPath(Name.trim());
+        await CreateEntry(RootName, FullPath, IsDirectory);
+
+        if (Users.length > 0 || Groups.length > 0) {
+          await SetLockApi(RootName, FullPath, Users, Groups);
+        }
+
+        await Reload();
+        OnEntryCreated();
+      } else if (ModalConfig.Mode === "editLock") {
+        await SetLockApi(RootName, ModalConfig.TargetPath, Users, Groups);
+        await Reload();
+      }
+
+      SetModalConfig(null);
+    } catch (Error) {
+      window.alert(Error.message);
+    }
+  }
+
   return (
     <div className="DirectoryPane">
       <div className="PreviewToolbar">
-        <button onClick={HandleCreateFile}>New File</button>
-        <button onClick={HandleCreateDirectory}>New Directory</button>
+        <button onClick={OpenCreateFileModal}>New File</button>
+        <button onClick={OpenCreateDirectoryModal}>New Directory</button>
       </div>
       {LoadError && <div className="SidebarError">{LoadError}</div>}
       <div className="DirectoryList">
@@ -122,6 +158,13 @@ export default function DirectoryPane({
             </span>
             <span className="TreeLabel">{Entry.Name}</span>
             <span className="TreeRowActions">
+              <button
+                className="TreeRowActionButton"
+                onClick={(Event) => HandleRequestLockEdit(Event, Entry)}
+                title="Access control"
+              >
+                🔒
+              </button>
               <button
                 className="TreeRowActionButton"
                 onClick={(Event) => HandleRename(Event, Entry)}
@@ -143,6 +186,42 @@ export default function DirectoryPane({
           <div className="DirectoryEmpty">Empty directory.</div>
         )}
       </div>
+
+      {ModalConfig && ModalConfig.Mode === "createFile" && (
+        <AccessModal
+          Title={`New file in ${DirectoryPath || "root"}`}
+          ShowNameField
+          NamePlaceholder="Notes.md"
+          InitialUsers={[]}
+          InitialGroups={[]}
+          ConfirmLabel="Create"
+          OnConfirm={HandleModalConfirm}
+          OnCancel={() => SetModalConfig(null)}
+        />
+      )}
+      {ModalConfig && ModalConfig.Mode === "createDirectory" && (
+        <AccessModal
+          Title={`New directory in ${DirectoryPath || "root"}`}
+          ShowNameField
+          NamePlaceholder="MyFolder"
+          InitialUsers={[]}
+          InitialGroups={[]}
+          ConfirmLabel="Create"
+          OnConfirm={HandleModalConfirm}
+          OnCancel={() => SetModalConfig(null)}
+        />
+      )}
+      {ModalConfig && ModalConfig.Mode === "editLock" && (
+        <AccessModal
+          Title={`Access for "${ModalConfig.EntryName}"`}
+          ShowNameField={false}
+          InitialUsers={ModalConfig.InitialUsers}
+          InitialGroups={ModalConfig.InitialGroups}
+          ConfirmLabel="Save"
+          OnConfirm={HandleModalConfirm}
+          OnCancel={() => SetModalConfig(null)}
+        />
+      )}
     </div>
   );
 }
diff --git a/Frontend/src/Components/PreviewPane.jsx b/Frontend/src/Components/PreviewPane.jsx
index 9f8140e..88e1f8a 100644
--- a/Frontend/src/Components/PreviewPane.jsx
+++ b/Frontend/src/Components/PreviewPane.jsx
@@ -7,7 +7,7 @@ import { json } from "@codemirror/lang-json";
 import MarkdownIt from "markdown-it";
 import MarkdownItTaskLists from "markdown-it-task-lists";
 
-import { FetchBlame, FetchFile, GetFileUrl, GetRawFileUrl, SaveFile } from "../Api.js";
+import { FetchBlame, FetchFile, GetAvatarUrl, GetFileUrl, GetRawFileUrl, SaveFile } from "../Api.js";
 
 const MarkdownRenderer = new MarkdownIt({ breaks: true }).use(MarkdownItTaskLists, {
   enabled: true,
@@ -90,26 +90,45 @@ function GetLanguageExtension(FileType) {
 }
 
 class BlameMarker extends GutterMarker {
-  constructor(ShortLabel, Title) {
+  constructor(Mode, Content, Colour, Title) {
     super();
-    this.ShortLabel = ShortLabel;
+    this.Mode = Mode;
+    this.Content = Content;
+    this.Colour = Colour;
     this.Title = Title;
   }
 
   eq(Other) {
-    return this.ShortLabel === Other.ShortLabel && this.Title === Other.Title;
+    return (
+      this.Mode === Other.Mode &&
+      this.Content === Other.Content &&
+      this.Colour === Other.Colour &&
+      this.Title === Other.Title
+    );
   }
 
   toDOM() {
+    if (this.Mode === "avatar") {
+      const Image = document.createElement("img");
+      Image.className = "BlameGutterAvatar";
+      Image.src = this.Content;
+      Image.title = this.Title;
+      Image.alt = "";
+      return Image;
+    }
+
     const Element = document.createElement("span");
-    Element.className = "BlameGutterMarker";
-    Element.textContent = this.ShortLabel;
+    Element.className = `BlameGutterMarker${this.Mode === "hidden" ? " BlameGutterHidden" : ""}`;
+    Element.textContent = this.Content;
     Element.title = this.Title;
+    if (this.Colour) {
+      Element.style.color = `var(--${this.Colour})`;
+    }
     return Element;
   }
 }
 
-function BuildBlameGutter(BlameMap) {
+function BuildBlameGutter(BlameMap, ShowAvatars) {
   return gutter({
     class: "BlameGutter",
     lineMarker(view, line) {
@@ -117,9 +136,18 @@ function BuildBlameGutter(BlameMap) {
       const Entry = BlameMap[String(LineNumber)];
       if (!Entry) return null;
 
-      const ShortLabel = Entry.Username.slice(0, 6);
+      if (Entry.Hidden) {
+        const Title = Entry.Timestamp ? new Date(Entry.Timestamp).toLocaleString() : "";
+        return new BlameMarker("hidden", "•••", null, Title);
+      }
+
       const Title = `${Entry.Username} — ${new Date(Entry.Timestamp).toLocaleString()}`;
-      return new BlameMarker(ShortLabel, Title);
+
+      if (ShowAvatars && Entry.HasAvatar) {
+        return new BlameMarker("avatar", GetAvatarUrl(Entry.Username), null, Title);
+      }
+
+      return new BlameMarker("text", Entry.Username.slice(0, 6), Entry.Colour, Title);
     },
   });
 }
@@ -130,6 +158,7 @@ export default function PreviewPane({
   FileType,
   OnNavigateLink,
   ShowGitBlame,
+  ShowBlameAvatars,
   StickyToolbar,
 }) {
   const [Content, SetContent] = useState("");
@@ -271,7 +300,7 @@ export default function PreviewPane({
           height="100%"
           extensions={[
             ...GetLanguageExtension(FileType),
-            ...(ShowGitBlame ? [BuildBlameGutter(BlameMap)] : []),
+            ...(ShowGitBlame ? [BuildBlameGutter(BlameMap, ShowBlameAvatars)] : []),
           ]}
           onChange={SetContent}
           theme="dark"
diff --git a/Frontend/src/Components/SettingsPanel.jsx b/Frontend/src/Components/SettingsPanel.jsx
index c14dd02..de09ea8 100644
--- a/Frontend/src/Components/SettingsPanel.jsx
+++ b/Frontend/src/Components/SettingsPanel.jsx
@@ -1,8 +1,13 @@
 import React, { useEffect, useState } from "react";
 
 import {
+  ChangePassword,
+  CreateGroupApi,
   CreateUserAccount,
+  DeleteGroupApi,
   DeleteTheme,
+  FetchGroups,
+  FetchLocks,
   FetchProfileColourOptions,
   FetchSettings,
   FetchTheme,
@@ -10,9 +15,12 @@ import {
   FetchUsers,
   GetAvatarUrl,
   Logout,
+  RemoveLock,
   SaveSettings,
   SaveTheme,
+  SetGroupMembersApi,
   UpdateProfileColour,
+  UpdateUsername,
   UploadAvatar,
 } from "../Api.js";
 import Switch from "./Switch.jsx";
@@ -46,12 +54,32 @@ export default function SettingsPanel({
   const [ProfileError, SetProfileError] = useState(null);
   const [AvatarNonce, SetAvatarNonce] = useState(0);
 
+  const [UsernameField, SetUsernameField] = useState("");
+  const [UsernameError, SetUsernameError] = useState(null);
+  const [CurrentPasswordField, SetCurrentPasswordField] = useState("");
+  const [NewPasswordField, SetNewPasswordField] = useState("");
+  const [PasswordError, SetPasswordError] = useState(null);
+  const [PasswordChanged, SetPasswordChanged] = useState(false);
+
+  const [Locks, SetLocksList] = useState(null);
+  const [LockError, SetLockError] = useState(null);
+
+  const [Groups, SetGroupsList] = useState(null);
+  const [NewGroupName, SetNewGroupName] = useState("");
+  const [GroupError, SetGroupError] = useState(null);
+  const [ExpandedGroup, SetExpandedGroup] = useState(null);
+
   useEffect(() => {
     FetchSettings().then(SetSettings);
     FetchThemeNames().then(SetThemeNames);
     FetchProfileColourOptions().then(SetColourOptions);
+    if (CurrentUser) {
+      SetUsernameField(CurrentUser.Username);
+    }
     if (CurrentUser && CurrentUser.IsAdmin) {
       FetchUsers().then(SetUsers);
+      FetchLocks().then(SetLocksList);
+      FetchGroups().then(SetGroupsList);
     }
   }, [CurrentUser]);
 
@@ -181,6 +209,86 @@ export default function SettingsPanel({
     }
   }
 
+  async function HandleChangeUsername() {
+    SetUsernameError(null);
+
+    if (!UsernameField.trim() || UsernameField.trim() === CurrentUser.Username) return;
+
+    try {
+      const Updated = await UpdateUsername(UsernameField.trim());
+      OnProfileUpdated(Updated);
+    } catch (Error) {
+      SetUsernameError(Error.message);
+    }
+  }
+
+  async function HandleChangePassword() {
+    SetPasswordError(null);
+    SetPasswordChanged(false);
+
+    try {
+      await ChangePassword(CurrentPasswordField, NewPasswordField);
+      SetCurrentPasswordField("");
+      SetNewPasswordField("");
+      SetPasswordChanged(true);
+    } catch (Error) {
+      SetPasswordError(Error.message);
+    }
+  }
+
+  async function HandleUnlock(Lock) {
+    SetLockError(null);
+    try {
+      await RemoveLock(Lock.Root, Lock.Path);
+      const Updated = await FetchLocks();
+      SetLocksList(Updated);
+    } catch (Error) {
+      SetLockError(Error.message);
+    }
+  }
+
+  async function HandleCreateGroup() {
+    SetGroupError(null);
+
+    try {
+      await CreateGroupApi(NewGroupName.trim());
+      const Updated = await FetchGroups();
+      SetGroupsList(Updated);
+      SetNewGroupName("");
+    } catch (Error) {
+      SetGroupError(Error.message);
+    }
+  }
+
+  async function HandleDeleteGroup(Name) {
+    if (!window.confirm(`Delete group "${Name}"? This can't be undone.`)) return;
+
+    SetGroupError(null);
+    try {
+      await DeleteGroupApi(Name);
+      const Updated = await FetchGroups();
+      SetGroupsList(Updated);
+    } catch (Error) {
+      SetGroupError(Error.message);
+    }
+  }
+
+  async function HandleToggleGroupMember(Group, Username) {
+    const CurrentMembers = Group.Members || [];
+    const NewMembers = CurrentMembers.includes(Username)
+      ? CurrentMembers.filter((Member) => Member !== Username)
+      : [...CurrentMembers, Username];
+
+    SetGroupError(null);
+    try {
+      await SetGroupMembersApi(Group.Name, NewMembers);
+      const Updated = await FetchGroups();
+      SetGroupsList(Updated);
+    } catch (Error) {
+      SetGroupError(Error.message);
+    }
+  }
+
   return (
     <div className="SettingsOverlay" onClick={OnClose}>
       <div className="SettingsModal" onClick={(Event) => Event.stopPropagation()}>
@@ -245,6 +353,16 @@ export default function SettingsPanel({
             <Switch Checked={Settings.ShowGitBlame} OnChange={(Event) => UpdateField("ShowGitBlame", Event.target.checked)} />
           </div>
 
+          <div className="SettingsRowInline">
+            <label className="SettingsLabel">Show avatars instead of names in blame</label>
+            <Switch Checked={Settings.ShowBlameAvatars} OnChange={(Event) => UpdateField("ShowBlameAvatars", Event.target.checked)} />
+          </div>
+
+          <div className="SettingsRowInline">
+            <label className="SettingsLabel">Show my edits in others' blame view</label>
+            <Switch Checked={Settings.VisibleInBlame} OnChange={(Event) => UpdateField("VisibleInBlame", Event.target.checked)} />
+          </div>
+
           <div className="SettingsRowInline">
             <label className="SettingsLabel">Sticky edit/view/save toolbar</label>
             <Switch Checked={Settings.StickyToolbar} OnChange={(Event) => UpdateField("StickyToolbar", Event.target.checked)} />
@@ -352,6 +470,42 @@ export default function SettingsPanel({
               </span>
               <button onClick={HandleLogout}>Log out</button>
             </div>
+
+            <div className="SettingsRow">
+              <label className="SettingsLabel">Username</label>
+              <div className="SettingsRowInline">
+                <input
+                  type="text"
+                  value={UsernameField}
+                  onChange={(Event) => SetUsernameField(Event.target.value)}
+                />
+                <button onClick={HandleChangeUsername}>Save</button>
+              </div>
+              {UsernameError && <div className="SettingsSaveError">{UsernameError}</div>}
+              <div className="SettingsHint">
+                Renaming logs out any other devices/browsers you're signed in on — this one
+                stays signed in under the new name.
+              </div>
+            </div>
+
+            <div className="SettingsRow">
+              <label className="SettingsLabel">Change password</label>
+              <input
+                type="password"
+                placeholder="Current password"
+                value={CurrentPasswordField}
+                onChange={(Event) => SetCurrentPasswordField(Event.target.value)}
+              />
+              <input
+                type="password"
+                placeholder="New password"
+                value={NewPasswordField}
+                onChange={(Event) => SetNewPasswordField(Event.target.value)}
+              />
+              <button onClick={HandleChangePassword}>Update password</button>
+              {PasswordChanged && <div className="SettingsHint">Password updated.</div>}
+              {PasswordError && <div className="SettingsSaveError">{PasswordError}</div>}
+            </div>
           </div>
 
           {CurrentUser && CurrentUser.IsAdmin && (
@@ -409,6 +563,86 @@ export default function SettingsPanel({
             </div>
           )}
 
+          {CurrentUser && CurrentUser.IsAdmin && (
+            <div className="SettingsSection">
+              <div className="SettingsSectionTitle">Locked Directories (admin)</div>
+              {Locks && Locks.length === 0 && (
+                <div className="SettingsHint">
+                  Nothing locked yet — use the 🔒 button next to any directory to lock it.
+                </div>
+              )}
+              {Locks &&
+                Locks.map((Lock, Index) => (
+                  <div className="SettingsRowInline" key={`${Lock.Root}:${Lock.Path}:${Index}`}>
+                    <span className="SettingsLabel">
+                      {Lock.Root}/{Lock.Path} —{" "}
+                      {[...(Lock.Users || []), ...(Lock.Groups || []).map((G) => `@${G}`)].join(
+                        ", "
+                      )}
+                    </span>
+                    <button onClick={() => HandleUnlock(Lock)}>Unlock</button>
+                  </div>
+                ))}
+              {LockError && <div className="SettingsSaveError">{LockError}</div>}
+            </div>
+          )}
+
+          {CurrentUser && CurrentUser.IsAdmin && (
+            <div className="SettingsSection">
+              <div className="SettingsSectionTitle">Groups (admin)</div>
+              {Groups &&
+                Groups.map((Group) => (
+                  <div key={Group.Name} className="GroupRow">
+                    <div className="SettingsRowInline">
+                      <span className="SettingsLabel">
+                        {Group.Name} ({(Group.Members || []).length})
+                      </span>
+                      <div className="SettingsRowInline">
+                        <button
+                          onClick={() =>
+                            SetExpandedGroup(ExpandedGroup === Group.Name ? null : Group.Name)
+                          }
+                        >
+                          {ExpandedGroup === Group.Name ? "Hide" : "Members"}
+                        </button>
+                        {Group.Name !== "Admin" && (
+                          <button onClick={() => HandleDeleteGroup(Group.Name)}>Delete</button>
+                        )}
+                      </div>
+                    </div>
+                    {ExpandedGroup === Group.Name && (
+                      <div className="AccessPickerList GroupMemberList">
+                        {(Users || []).map((User) => (
+                          <label className="AccessPickerRow" key={User.Username}>
+                            <input
+                              type="checkbox"
+                              checked={(Group.Members || []).includes(User.Username)}
+                              onChange={() => HandleToggleGroupMember(Group, User.Username)}
+                            />
+                            <span
+                              className="ColourSwatchSmall"
+                              style={{ background: `var(--${User.Colour || "Purple"})` }}
+                            />
+                            <span>{User.Username}</span>
+                          </label>
+                        ))}
+                      </div>
+                    )}
+                  </div>
+                ))}
+              <div className="SettingsRowInline">
+                <input
+                  type="text"
+                  placeholder="New group name"
+                  value={NewGroupName}
+                  onChange={(Event) => SetNewGroupName(Event.target.value)}
+                />
+                <button onClick={HandleCreateGroup}>Create group</button>
+              </div>
+              {GroupError && <div className="SettingsSaveError">{GroupError}</div>}
+            </div>
+          )}
+
           {SaveError && <div className="SettingsSaveError">{SaveError}</div>}
         </div>
 
diff --git a/Frontend/src/Components/Sidebar.jsx b/Frontend/src/Components/Sidebar.jsx
index bdc12be..98846be 100644
--- a/Frontend/src/Components/Sidebar.jsx
+++ b/Frontend/src/Components/Sidebar.jsx
@@ -1,7 +1,17 @@
 import React, { useEffect, useState } from "react";
 
-import { CreateEntry, DeleteEntry, FetchTree, GetAvatarUrl, MoveEntry, RenameEntry } from "../Api.js";
+import {
+  CreateEntry,
+  DeleteEntry,
+  FetchLock,
+  FetchTree,
+  GetAvatarUrl,
+  MoveEntry,
+  RenameEntry,
+  SetLock as SetLockApi,
+} from "../Api.js";
 import { GetFileIcon, GetFolderIcon } from "../IconStyle.js";
+import AccessModal from "./AccessModal.jsx";
 
 function TreeNode({
   RootName,
@@ -14,6 +24,7 @@ function TreeNode({
   OnBrowseDirectory,
   OnEntryRenamed,
   OnEntryDeleted,
+  OnRequestLockEdit,
   UseHyphenBullets,
   UseAsciiFolderIcons,
   NavigateIntoDirectories,
@@ -103,6 +114,11 @@ function TreeNode({
     }
   }
 
+  function HandleLockClick(Event) {
+    Event.stopPropagation();
+    OnRequestLockEdit(FullPath, Entry.Name);
+  }
+
   return (
     <div className="TreeNode">
       <div
@@ -118,6 +134,9 @@ function TreeNode({
         </span>
         <span className="TreeLabel">{Entry.Name}</span>
         <span className="TreeRowActions">
+          <button className="TreeRowActionButton" onClick={HandleLockClick} title="Access control">
+            🔒
+          </button>
           <button className="TreeRowActionButton" onClick={HandleRename} title="Rename / move">
             ✎
           </button>
@@ -141,6 +160,7 @@ function TreeNode({
               OnBrowseDirectory={OnBrowseDirectory}
               OnEntryRenamed={OnEntryRenamed}
               OnEntryDeleted={OnEntryDeleted}
+              OnRequestLockEdit={OnRequestLockEdit}
               UseHyphenBullets={UseHyphenBullets}
               UseAsciiFolderIcons={UseAsciiFolderIcons}
               NavigateIntoDirectories={NavigateIntoDirectories}
@@ -207,6 +227,7 @@ export default function Sidebar({
 }) {
   const [RootEntries, SetRootEntries] = useState([]);
   const [LoadError, SetLoadError] = useState(null);
+  const [ModalConfig, SetModalConfig] = useState(null);
 
   useEffect(() => {
     if (RootName) {
@@ -221,39 +242,53 @@ export default function Sidebar({
     return CurrentDirectoryPath ? `${CurrentDirectoryPath}/${Name}` : Name;
   }
 
-  async function HandleCreateFile() {
-    const Name = window.prompt(
-      `New file name in ${CurrentDirectoryPath || "root"} (e.g. Notes.md):`
-    );
-    if (!Name) return;
+  function OpenCreateFileModal() {
+    SetModalConfig({ Mode: "createFile" });
+  }
 
+  function OpenCreateDirectoryModal() {
+    SetModalConfig({ Mode: "createDirectory" });
+  }
+
+  async function HandleRequestLockEdit(FullPath, EntryName) {
     try {
-      await CreateEntry(RootName, JoinPath(Name), false);
-      OnEntryCreated();
+      const Existing = await FetchLock(RootName, FullPath);
+      SetModalConfig({
+        Mode: "editLock",
+        TargetPath: FullPath,
+        EntryName,
+        InitialUsers: (Existing && Existing.Users) || [],
+        InitialGroups: (Existing && Existing.Groups) || [],
+      });
     } catch (Error) {
-      SetLoadError(Error.message);
+      window.alert(Error.message);
     }
   }
 
-  async function HandleCreateDirectory() {
-    const Name = window.prompt(`New directory name in ${CurrentDirectoryPath || "root"}:`);
-    if (!Name) return;
-
+  async function HandleModalConfirm(Name, Users, Groups) {
     try {
-      await CreateEntry(RootName, JoinPath(Name), true);
-      OnEntryCreated();
+      if (ModalConfig.Mode === "createFile" || ModalConfig.Mode === "createDirectory") {
+        if (!Name || !Name.trim()) return;
+
+        const IsDirectory = ModalConfig.Mode === "createDirectory";
+        const FullPath = JoinPath(Name.trim());
+        await CreateEntry(RootName, FullPath, IsDirectory);
+
+        if (Users.length > 0 || Groups.length > 0) {
+          await SetLockApi(RootName, FullPath, Users, Groups);
+        }
+
+        OnEntryCreated();
+      } else if (ModalConfig.Mode === "editLock") {
+        await SetLockApi(RootName, ModalConfig.TargetPath, Users, Groups);
+      }
+
+      SetModalConfig(null);
     } catch (Error) {
-      SetLoadError(Error.message);
+      window.alert(Error.message);
     }
   }
 
-  const NewEntryButtons = (
-    <div className={`SidebarNewEntry${NewEntryButtonsAtTop ? " SidebarNewEntryTop" : ""}`}>
-      <button onClick={HandleCreateFile}>New File</button>
-      <button onClick={HandleCreateDirectory}>New Directory</button>
-    </div>
-  );
-
   return (
     <div className="Sidebar">
       <div className="SidebarHeader">
@@ -267,7 +302,12 @@ export default function Sidebar({
           </button>
         </span>
       </div>
-      {NewEntryButtonsAtTop && NewEntryButtons}
+      {NewEntryButtonsAtTop && (
+        <div className="SidebarNewEntry SidebarNewEntryTop">
+          <button onClick={OpenCreateFileModal}>New File</button>
+          <button onClick={OpenCreateDirectoryModal}>New Directory</button>
+        </div>
+      )}
       {LoadError && <div className="SidebarError">{LoadError}</div>}
       <div className="SidebarTree">
         {RootEntries.map((Entry) => (
@@ -283,6 +323,7 @@ export default function Sidebar({
             OnBrowseDirectory={OnBrowseDirectory}
             OnEntryRenamed={OnEntryRenamed}
             OnEntryDeleted={OnEntryDeleted}
+            OnRequestLockEdit={HandleRequestLockEdit}
             UseHyphenBullets={UseHyphenBullets}
             UseAsciiFolderIcons={UseAsciiFolderIcons}
             NavigateIntoDirectories={NavigateIntoDirectories}
@@ -290,7 +331,48 @@ export default function Sidebar({
           />
         ))}
       </div>
-      {!NewEntryButtonsAtTop && NewEntryButtons}
+      {!NewEntryButtonsAtTop && (
+        <div className="SidebarNewEntry">
+          <button onClick={OpenCreateFileModal}>New File</button>
+          <button onClick={OpenCreateDirectoryModal}>New Directory</button>
+        </div>
+      )}
+
+      {ModalConfig && ModalConfig.Mode === "createFile" && (
+        <AccessModal
+          Title={`New file in ${CurrentDirectoryPath || "root"}`}
+          ShowNameField
+          NamePlaceholder="Notes.md"
+          InitialUsers={[]}
+          InitialGroups={[]}
+          ConfirmLabel="Create"
+          OnConfirm={HandleModalConfirm}
+          OnCancel={() => SetModalConfig(null)}
+        />
+      )}
+      {ModalConfig && ModalConfig.Mode === "createDirectory" && (
+        <AccessModal
+          Title={`New directory in ${CurrentDirectoryPath || "root"}`}
+          ShowNameField
+          NamePlaceholder="MyFolder"
+          InitialUsers={[]}
+          InitialGroups={[]}
+          ConfirmLabel="Create"
+          OnConfirm={HandleModalConfirm}
+          OnCancel={() => SetModalConfig(null)}
+        />
+      )}
+      {ModalConfig && ModalConfig.Mode === "editLock" && (
+        <AccessModal
+          Title={`Access for "${ModalConfig.EntryName}"`}
+          ShowNameField={false}
+          InitialUsers={ModalConfig.InitialUsers}
+          InitialGroups={ModalConfig.InitialGroups}
+          ConfirmLabel="Save"
+          OnConfirm={HandleModalConfirm}
+          OnCancel={() => SetModalConfig(null)}
+        />
+      )}
     </div>
   );
 }
diff --git a/Frontend/src/Styles/Theme.css b/Frontend/src/Styles/Theme.css
index 33e98c1..a65fb69 100644
--- a/Frontend/src/Styles/Theme.css
+++ b/Frontend/src/Styles/Theme.css
@@ -454,6 +454,20 @@ img,
   white-space: nowrap;
 }
 
+.BlameGutterHidden {
+  color: var(--TextMuted);
+  opacity: 0.6;
+}
+
+.BlameGutterAvatar {
+  width: 14px;
+  height: 14px;
+  border-radius: 50%;
+  object-fit: cover;
+  margin: 0 4px;
+  vertical-align: middle;
+}
+
 .PreviewMedia img,
 .PreviewMedia video {
   margin: auto;
@@ -747,6 +761,76 @@ img,
   font-size: 13px;
 }
 
+.SettingsHint {
+  color: var(--TextMuted);
+  font-size: 12px;
+}
+
+.AccessPicker {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+
+.AccessPicker input[type="text"] {
+  background: var(--SurfaceAlt);
+  color: var(--Text);
+  border: 1px solid var(--Border);
+  border-radius: 4px;
+  padding: 6px 8px;
+  font-family: inherit;
+}
+
+.AccessPickerList {
+  max-height: 160px;
+  overflow-y: auto;
+  border: 1px solid var(--Border);
+  border-radius: 4px;
+  padding: 4px;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+
+.AccessPickerRow {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 4px 6px;
+  border-radius: 3px;
+  cursor: pointer;
+  font-size: 13px;
+}
+
+.AccessPickerRow:hover {
+  background: var(--SurfaceAlt);
+}
+
+.AccessPickerType {
+  color: var(--Purple);
+  font-size: 11px;
+  border: 1px solid var(--Purple);
+  border-radius: 3px;
+  padding: 0 4px;
+}
+
+.AccessPickerEmpty {
+  color: var(--TextMuted);
+  font-size: 13px;
+  padding: 4px 6px;
+}
+
+.GroupRow {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  padding: 4px 0;
+}
+
+.GroupMemberList {
+  margin-left: 8px;
+}
+
 /* Login screen */
 
 .LoginScreen {
diff --git a/README.md b/README.md
index c4783d3..af8f49c 100644
--- a/README.md
+++ b/README.md
@@ -139,3 +139,37 @@ own icon/entry in ZimaOS's app store the way bundled apps do — that would
 need a CasaOS-format AppStore manifest (icon, category, metadata) submitted
 separately, which is a reasonable next step if you want it to feel fully
 native rather than "a compose file I pasted in."
+
+## Groups and access control
+
+Admin isn't a hardcoded flag — it's the built-in "Admin" group, which can't
+be deleted but is otherwise just a group like any other. Manage groups
+(create, delete, edit membership) from Settings → Groups (admin-only).
+
+Setting access on a file or directory is **not** admin-only — anyone can
+restrict a file or directory to specific users and/or groups, whether at
+creation time (the New File/New Directory dialog includes a search-and-
+checkbox picker) or afterwards via the 🔒 button next to any entry, in
+either the sidebar tree or the directory-browse pane. If you can currently
+see something, you're trusted to change who else can. Admins additionally
+bypass every restriction, so they can always troubleshoot.
+
+Restricting is per-file-or-directory — locking a directory covers everything
+inside it automatically (there's only ever one restriction record per locked
+directory; reaching anything underneath still requires being permitted on
+that ancestor), while locking an individual file affects only that file.
+
+Anyone without access gets a plain 404, both for direct requests and for
+that entry showing up in a directory listing — a restricted item's existence
+isn't revealed to people who can't see it. Admins get a global overview of
+every current restriction from Settings → Locked Directories.
+
+## Blame privacy
+
+Each person can turn off "Show my edits in others' blame view" in their own
+Settings. When that's off, other users still see that lines were changed —
+just with the identity redacted, rather than attributing it to someone who
+asked not to be shown. You can always see your own attribution regardless of
+this setting. There's also a per-viewer toggle for showing avatars instead
+of usernames in the blame gutter, using each author's chosen colour either
+way.