diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index dc4ff58..f319bcc 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -1,5 +1,6 @@
 import { Navigate, Route, Routes } from "react-router-dom";
 import { AuthProvider, RequireAdmin, RequireAuth } from "./auth/AuthContext";
+import { AppShell } from "./components/app-shell";
 import { ErrorBoundary } from "./components/ErrorBoundary";
 import { Toaster } from "./components/Toaster";
 import { ThemeProvider } from "./components/theme";
@@ -17,13 +18,16 @@ export default function App() {
           <Routes>
             <Route path="/login" element={<Login />} />
             <Route
-              path="/"
               element={
                 <RequireAuth>
-                  <Shelf />
+                  <AppShell />
                 </RequireAuth>
               }
-            />
+            >
+              <Route path="/" element={<Shelf />} />
+              <Route path="/admin/users" element={<RequireAdmin><AdminUsers /></RequireAdmin>} />
+              <Route path="/admin/libraries" element={<RequireAdmin><AdminLibraries /></RequireAdmin>} />
+            </Route>
             <Route
               path="/book/:id"
               element={
@@ -32,26 +36,6 @@ export default function App() {
                 </RequireAuth>
               }
             />
-            <Route
-              path="/admin/users"
-              element={
-                <RequireAuth>
-                  <RequireAdmin>
-                    <AdminUsers />
-                  </RequireAdmin>
-                </RequireAuth>
-              }
-            />
-            <Route
-              path="/admin/libraries"
-              element={
-                <RequireAuth>
-                  <RequireAdmin>
-                    <AdminLibraries />
-                  </RequireAdmin>
-                </RequireAuth>
-              }
-            />
             <Route path="*" element={<Navigate to="/" replace />} />
           </Routes>
           <Toaster />
diff --git a/frontend/src/components/app-shell.tsx b/frontend/src/components/app-shell.tsx
new file mode 100644
index 0000000..32a78d7
--- /dev/null
+++ b/frontend/src/components/app-shell.tsx
@@ -0,0 +1,131 @@
+import { useQuery } from "@tanstack/react-query";
+import { BookMarked, BookOpen, FolderCog, LogOut, Users } from "lucide-react";
+import { NavLink, Outlet, useLocation } from "react-router-dom";
+import { api } from "@/api/client";
+import { useAuth } from "@/auth/AuthContext";
+import { Button } from "@/components/ui/button";
+import { DropdownMenu, DropdownMenuContent, DropdownMenuItem, DropdownMenuLabel, DropdownMenuSeparator, DropdownMenuTrigger } from "@/components/ui/dropdown-menu";
+import { Separator } from "@/components/ui/separator";
+import { ThemeToggle } from "./theme-toggle";
+import { cn } from "@/lib/utils";
+import type { ReactNode } from "react";
+
+function Brand({ compact }: { compact?: boolean }) {
+  return (
+    <NavLink to="/" className="flex h-12 shrink-0 items-center gap-2 rounded-md px-3 focus-visible:outline-2 focus-visible:outline-offset-2">
+      <span className="grid size-6 place-items-center rounded bg-accent text-accent-foreground">
+        <BookMarked className="size-4" />
+      </span>
+      {!compact && <span className="text-[15px] font-semibold tracking-tight">BookLib</span>}
+    </NavLink>
+  );
+}
+
+function NavItem({ to, icon, label, search }: { to: string; icon: ReactNode; label: string; search?: string }) {
+  return (
+    <NavLink
+      to={to + (search ?? "")}
+      className={({ isActive }) =>
+        cn(
+          "flex items-center gap-3 rounded-md px-3 py-2 text-sm text-muted-foreground transition-colors hover:bg-secondary hover:text-foreground",
+          isActive && "bg-secondary font-medium text-foreground",
+        )
+      }
+    >
+      {icon}
+      <span className="hidden lg:inline">{label}</span>
+    </NavLink>
+  );
+}
+
+export function AppShell() {
+  const { user, isAdmin, logout } = useAuth();
+  const loc = useLocation();
+  const libsQ = useQuery({ queryKey: ["libraries"], queryFn: api.listLibraries });
+  const libs = libsQ.data ?? [];
+
+  const account = (
+    <DropdownMenu>
+      <DropdownMenuTrigger asChild>
+        <Button variant="ghost" className="gap-2 px-2">
+          <span className="grid size-7 place-items-center rounded-full bg-accent/15 text-xs font-semibold text-accent">
+            {Array.from(user?.username ?? "?")[0]?.toUpperCase()}
+          </span>
+          <span className="hidden max-w-28 truncate text-sm lg:inline">{user?.username}</span>
+        </Button>
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="end">
+        <DropdownMenuLabel>{user?.username}{isAdmin ? " · admin" : ""}</DropdownMenuLabel>
+        <DropdownMenuSeparator />
+        <DropdownMenuItem asChild>
+          <span className="cursor-pointer" onClick={logout}>
+            <LogOut /> 退出登录
+          </span>
+        </DropdownMenuItem>
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+
+  return (
+    <div className="flex h-full">
+      {/* 桌面/平板侧栏;lg 全文标签,md 图标栏 */}
+      <aside className="flex w-14 shrink-0 flex-col gap-1 border-r bg-card/60 p-2 lg:w-60">
+        <Brand compact />
+        <nav aria-label="主导航" className="flex flex-col gap-1">
+          <NavItem to="/" icon={<BookOpen className="size-4 shrink-0" />} label="书架" />
+          {isAdmin && (
+            <>
+              <NavItem to="/admin/libraries" icon={<FolderCog className="size-4 shrink-0" />} label="库管理" />
+              <NavItem to="/admin/users" icon={<Users className="size-4 shrink-0" />} label="用户管理" />
+            </>
+          )}
+        </nav>
+        {libs.length > 0 && (
+          <div className="mt-3 hidden min-h-0 flex-1 flex-col lg:flex">
+            <p className="px-3 pb-1 text-[11px] font-medium uppercase tracking-wider text-muted-foreground">书库</p>
+            <div className="min-h-0 flex-1 overflow-y-auto">
+              <NavItem to="/" search="?lib=0" icon={<span className="size-1.5 shrink-0 rounded-full bg-muted-foreground/50" />} label="全部" />
+              {libs.map((l) => (
+                <NavItem key={l.id} to="/" search={`?lib=${l.id}`} icon={<span className="size-1.5 shrink-0 rounded-full bg-accent/60" />} label={l.name} />
+              ))}
+            </div>
+          </div>
+        )}
+        <Separator className="my-2 hidden lg:block" />
+        <div className="mt-auto hidden items-center justify-between px-1 lg:flex">
+          <ThemeToggle />
+          {account}
+        </div>
+      </aside>
+
+      <div className="flex min-w-0 flex-1 flex-col">
+        {/* 移动端顶栏 */}
+        <header className="flex h-12 shrink-0 items-center justify-between border-b bg-card/60 px-3 lg:hidden">
+          <Brand />
+          <div className="flex items-center gap-1">
+            <ThemeToggle />
+            {account}
+          </div>
+        </header>
+        <main key={loc.pathname} className="min-h-0 flex-1 overflow-y-auto">
+          <Outlet />
+        </main>
+        {/* 移动端底 Tab */}
+        <nav aria-label="底部导航" className="flex h-14 shrink-0 items-stretch border-t bg-card/90 backdrop-blur md:hidden">
+          <TabItem to="/" icon={<BookOpen className="size-5" />} label="书架" search="?lib=0" />
+          {isAdmin && <TabItem to="/admin/libraries" icon={<FolderCog className="size-5" />} label="库管理" />}
+          {isAdmin && <TabItem to="/admin/users" icon={<Users className="size-5" />} label="用户" />}
+        </nav>
+      </div>
+    </div>
+  );
+}
+
+function TabItem({ to, icon, label, search }: { to: string; icon: ReactNode; label: string; search?: string }) {
+  return (
+    <NavLink to={to + (search ?? "")} className={({ isActive }) => cn("flex flex-col items-center justify-center gap-0.5 text-[11px] text-muted-foreground", isActive && "text-accent")}>
+      {icon}
+      {label}
+    </NavLink>
+  );
+}
diff --git a/frontend/src/components/theme-toggle.tsx b/frontend/src/components/theme-toggle.tsx
new file mode 100644
index 0000000..53a8dd7
--- /dev/null
+++ b/frontend/src/components/theme-toggle.tsx
@@ -0,0 +1,32 @@
+import { Check, Monitor, Moon, Sun } from "lucide-react";
+import { useTheme, type Theme } from "./theme";
+import { DropdownMenu, DropdownMenuContent, DropdownMenuItem, DropdownMenuTrigger } from "@/components/ui/dropdown-menu";
+import { Button } from "@/components/ui/button";
+
+const ITEMS: { v: Theme; label: string; icon: typeof Sun }[] = [
+  { v: "light", label: "浅色", icon: Sun },
+  { v: "dark", label: "深色", icon: Moon },
+  { v: "system", label: "跟随系统", icon: Monitor },
+];
+
+export function ThemeToggle() {
+  const { theme, setTheme } = useTheme();
+  return (
+    <DropdownMenu>
+      <DropdownMenuTrigger asChild>
+        <Button variant="ghost" size="icon" aria-label="切换主题" aria-pressed="false">
+          {theme === "dark" ? <Moon className="size-4" /> : theme === "light" ? <Sun className="size-4" /> : <Monitor className="size-4" />}
+        </Button>
+      </DropdownMenuTrigger>
+      <DropdownMenuContent align="end">
+        {ITEMS.map(({ v, label, icon: Icon }) => (
+          <DropdownMenuItem key={v} onClick={() => setTheme(v)}>
+            <Icon />
+            {label}
+            {theme === v && <Check className="ml-auto size-4" />}
+          </DropdownMenuItem>
+        ))}
+      </DropdownMenuContent>
+    </DropdownMenu>
+  );
+}