diff --git a/apps/web/src/layout/AppLayout.tsx b/apps/web/src/layout/AppLayout.tsx
index c274dd9..0a296ea 100644
--- a/apps/web/src/layout/AppLayout.tsx
+++ b/apps/web/src/layout/AppLayout.tsx
@@ -5,12 +5,19 @@ import { usePersistentState } from '../lib/use-persistent-state';
 import { Footer } from './Footer';
 import { SidebarChromeContext } from './sidebar-chrome';
 import { Sidebar } from './Sidebar';
+import { clampSidebarWidth, SIDEBAR_DEFAULT_WIDTH_REM, SidebarResizer } from './SidebarResizer';
 import { TopBar } from './TopBar';
 
 export function AppLayout(): React.JSX.Element {
   const [sidebarCollapsed, setSidebarCollapsed] = usePersistentState('ui.sidebar.collapsed', false);
+  const [sidebarWidth, setSidebarWidth] = usePersistentState(
+    'ui.sidebar.width',
+    SIDEBAR_DEFAULT_WIDTH_REM,
+  );
   const [forcedHidden, setForcedHidden] = useState(false);
   const collapsed = sidebarCollapsed || forcedHidden;
+  // Clamp on read too — the persisted value may predate a bounds change.
+  const widthRem = clampSidebarWidth(sidebarWidth);
 
   // Ctrl/Cmd+\ toggles the sidebar (same shortcut as Notion), regardless of
   // which element has focus.
@@ -32,8 +39,12 @@ export function AppLayout(): React.JSX.Element {
           sidebarCollapsed={collapsed}
           onToggleSidebar={() => setSidebarCollapsed(!sidebarCollapsed)}
         />
-        <div className="app-body">
+        <div
+          className="app-body"
+          style={{ '--sidebar-width': `${widthRem}rem` } as React.CSSProperties}
+        >
           <Sidebar collapsed={collapsed} />
+          {!collapsed && <SidebarResizer widthRem={widthRem} onResize={setSidebarWidth} />}
           <main className="main">
             <Outlet />
             <Footer />
diff --git a/apps/web/src/layout/SidebarResizer.tsx b/apps/web/src/layout/SidebarResizer.tsx
new file mode 100644
index 0000000..59f8fbf
--- /dev/null
+++ b/apps/web/src/layout/SidebarResizer.tsx
@@ -0,0 +1,86 @@
+import { useRef } from 'react';
+import { useTranslation } from 'react-i18next';
+
+/** Sidebar width bounds and default, in rem (issue #99). */
+export const SIDEBAR_MIN_WIDTH_REM = 12;
+export const SIDEBAR_MAX_WIDTH_REM = 32;
+export const SIDEBAR_DEFAULT_WIDTH_REM = 16;
+
+/** Step for keyboard adjustment, in rem. */
+const KEYBOARD_STEP_REM = 1;
+
+export function clampSidebarWidth(rem: number): number {
+  if (!Number.isFinite(rem)) return SIDEBAR_DEFAULT_WIDTH_REM;
+  return Math.min(SIDEBAR_MAX_WIDTH_REM, Math.max(SIDEBAR_MIN_WIDTH_REM, rem));
+}
+
+interface SidebarResizerProps {
+  widthRem: number;
+  onResize: (widthRem: number) => void;
+}
+
+/**
+ * Drag handle on the sidebar's right edge. Pointer-draggable, keyboard-
+ * adjustable (arrow keys, Home/End), double-click resets to the default.
+ */
+export function SidebarResizer({ widthRem, onResize }: SidebarResizerProps): React.JSX.Element {
+  const { t } = useTranslation();
+  const dragStart = useRef<{ pointerX: number; widthRem: number } | null>(null);
+
+  function remToPx(): number {
+    return parseFloat(getComputedStyle(document.documentElement).fontSize) || 16;
+  }
+
+  function handlePointerDown(event: React.PointerEvent<HTMLDivElement>): void {
+    // preventDefault (drag/selection guard) also swallows dblclick, so the
+    // double-click reset is detected via the click count here.
+    event.preventDefault();
+    if (event.detail >= 2) {
+      dragStart.current = null;
+      onResize(SIDEBAR_DEFAULT_WIDTH_REM);
+      return;
+    }
+    dragStart.current = { pointerX: event.clientX, widthRem };
+    event.currentTarget.setPointerCapture(event.pointerId);
+  }
+
+  function handlePointerMove(event: React.PointerEvent<HTMLDivElement>): void {
+    if (!dragStart.current) return;
+    const deltaRem = (event.clientX - dragStart.current.pointerX) / remToPx();
+    onResize(clampSidebarWidth(dragStart.current.widthRem + deltaRem));
+  }
+
+  function handlePointerUp(event: React.PointerEvent<HTMLDivElement>): void {
+    dragStart.current = null;
+    event.currentTarget.releasePointerCapture(event.pointerId);
+  }
+
+  function handleKeyDown(event: React.KeyboardEvent<HTMLDivElement>): void {
+    let next: number | null = null;
+    if (event.key === 'ArrowLeft') next = widthRem - KEYBOARD_STEP_REM;
+    else if (event.key === 'ArrowRight') next = widthRem + KEYBOARD_STEP_REM;
+    else if (event.key === 'Home') next = SIDEBAR_MIN_WIDTH_REM;
+    else if (event.key === 'End') next = SIDEBAR_MAX_WIDTH_REM;
+    if (next === null) return;
+    event.preventDefault();
+    onResize(clampSidebarWidth(next));
+  }
+
+  return (
+    <div
+      className="sidebar-resizer"
+      role="separator"
+      aria-orientation="vertical"
+      aria-label={t('layout.sidebar.resize')}
+      aria-valuenow={Math.round(widthRem)}
+      aria-valuemin={SIDEBAR_MIN_WIDTH_REM}
+      aria-valuemax={SIDEBAR_MAX_WIDTH_REM}
+      tabIndex={0}
+      onPointerDown={handlePointerDown}
+      onPointerMove={handlePointerMove}
+      onPointerUp={handlePointerUp}
+      onDoubleClick={() => onResize(SIDEBAR_DEFAULT_WIDTH_REM)}
+      onKeyDown={handleKeyDown}
+    />
+  );
+}
diff --git a/apps/web/src/styles/base.css b/apps/web/src/styles/base.css
index a44bd90..78d6d38 100644
--- a/apps/web/src/styles/base.css
+++ b/apps/web/src/styles/base.css
@@ -99,6 +99,22 @@ button {
   opacity: 0;
 }
 
+/* Drag handle on the sidebar's right edge (issue #99). */
+.sidebar-resizer {
+  flex-shrink: 0;
+  width: 6px;
+  margin-left: -3px;
+  cursor: col-resize;
+  touch-action: none;
+  background: transparent;
+}
+
+.sidebar-resizer:hover,
+.sidebar-resizer:focus-visible {
+  background: var(--color-accent);
+  outline: none;
+}
+
 .sidebar__hint {
   color: var(--color-text-muted);
   font-size: 0.9rem;
diff --git a/packages/shared/i18n/de/common.json b/packages/shared/i18n/de/common.json
index ebd970e..5f33908 100644
--- a/packages/shared/i18n/de/common.json
+++ b/packages/shared/i18n/de/common.json
@@ -3,6 +3,7 @@
     "sidebar": {
       "expand": "Seitenleiste einblenden",
       "collapse": "Seitenleiste ausblenden",
+      "resize": "Breite der Seitenleiste anpassen",
       "label": "Seiten",
       "placeholder": "Deine Teiche und Seiten erscheinen hier.",
       "empty": "Noch keine Seiten.",
diff --git a/packages/shared/i18n/en/common.json b/packages/shared/i18n/en/common.json
index 6121bff..0d6af6b 100644
--- a/packages/shared/i18n/en/common.json
+++ b/packages/shared/i18n/en/common.json
@@ -3,6 +3,7 @@
     "sidebar": {
       "expand": "Show sidebar",
       "collapse": "Hide sidebar",
+      "resize": "Resize sidebar",
       "label": "Pages",
       "placeholder": "Your ponds and pages will appear here.",
       "empty": "No pages yet.",