diff --git a/frontend/src/lib/components/HelpPopover.svelte b/frontend/src/lib/components/HelpPopover.svelte
new file mode 100644
index 00000000..e1d118ca
--- /dev/null
+++ b/frontend/src/lib/components/HelpPopover.svelte
@@ -0,0 +1,84 @@
+<script lang="ts">
+import type { Snippet } from 'svelte';
+
+type Placement = 'bottom' | 'top' | 'left' | 'right';
+
+type Props = {
+	label: string;
+	placement?: Placement;
+	children?: Snippet;
+};
+
+let { label, placement = 'bottom', children }: Props = $props();
+
+let open = $state(false);
+const popoverId = `help-popover-${Math.random().toString(36).slice(2)}`;
+let triggerEl: HTMLButtonElement | null = $state(null);
+
+function toggle() {
+	open = !open;
+}
+
+function close() {
+	open = false;
+	triggerEl?.focus();
+}
+
+$effect(() => {
+	if (!open) return;
+
+	function onKeyDown(e: KeyboardEvent) {
+		if (e.key === 'Escape') {
+			e.preventDefault();
+			close();
+		}
+	}
+
+	function onPointerDown(e: PointerEvent) {
+		if (triggerEl && (e.target === triggerEl || triggerEl.contains(e.target as Node))) return;
+		const popoverEl = document.getElementById(popoverId);
+		if (popoverEl && popoverEl.contains(e.target as Node)) return;
+		open = false;
+	}
+
+	document.addEventListener('keydown', onKeyDown);
+	document.addEventListener('pointerdown', onPointerDown);
+	return () => {
+		document.removeEventListener('keydown', onKeyDown);
+		document.removeEventListener('pointerdown', onPointerDown);
+	};
+});
+
+const placementClass: Record<Placement, string> = {
+	bottom: 'top-full mt-1.5 left-1/2 -translate-x-1/2',
+	top: 'bottom-full mb-1.5 left-1/2 -translate-x-1/2',
+	left: 'right-full mr-1.5 top-1/2 -translate-y-1/2',
+	right: 'left-full ml-1.5 top-1/2 -translate-y-1/2'
+};
+</script>
+
+<div class="relative inline-block">
+	<button
+		bind:this={triggerEl}
+		type="button"
+		aria-label={label}
+		aria-expanded={open}
+		aria-controls={popoverId}
+		onclick={toggle}
+		class="flex h-5 w-5 items-center justify-center rounded-full border border-line bg-muted font-sans text-[10px] font-bold text-ink-3 transition-colors hover:border-brand-navy hover:text-brand-navy"
+	>
+		?
+	</button>
+
+	{#if open}
+		<div
+			id={popoverId}
+			role="tooltip"
+			class="absolute z-50 w-64 rounded-sm border border-line bg-white p-3 font-sans text-sm text-ink shadow-md {placementClass[placement]}"
+		>
+			{#if children}
+				{@render children()}
+			{/if}
+		</div>
+	{/if}
+</div>
diff --git a/frontend/src/lib/components/HelpPopover.svelte.spec.ts b/frontend/src/lib/components/HelpPopover.svelte.spec.ts
new file mode 100644
index 00000000..b2e5ae16
--- /dev/null
+++ b/frontend/src/lib/components/HelpPopover.svelte.spec.ts
@@ -0,0 +1,77 @@
+import { describe, it, expect, afterEach, vi } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import HelpPopover from './HelpPopover.svelte';
+
+afterEach(cleanup);
+
+function renderPopover(label = 'Help') {
+	return render(HelpPopover, { props: { label } });
+}
+
+describe('HelpPopover — initial state', () => {
+	it('renders a trigger button with the given label', async () => {
+		renderPopover();
+		const btn = page.getByRole('button', { name: /Help/ });
+		await expect.element(btn).toBeInTheDocument();
+	});
+
+	it('starts closed: aria-expanded is false, popover not in DOM', async () => {
+		renderPopover();
+		const btn = page.getByRole('button', { name: /Help/ });
+		await expect.element(btn).toHaveAttribute('aria-expanded', 'false');
+		expect(document.querySelector('[role="tooltip"]')).toBeNull();
+	});
+});
+
+describe('HelpPopover — open / close interactions', () => {
+	it('opens on click: aria-expanded true, popover in DOM', async () => {
+		renderPopover();
+		await page.getByRole('button', { name: /Help/ }).click();
+		const btn = page.getByRole('button', { name: /Help/ });
+		await expect.element(btn).toHaveAttribute('aria-expanded', 'true');
+		expect(document.querySelector('[role="tooltip"]')).not.toBeNull();
+	});
+
+	it('closes on Esc key', async () => {
+		renderPopover();
+		await page.getByRole('button', { name: /Help/ }).click();
+		expect(document.querySelector('[role="tooltip"]')).not.toBeNull();
+
+		document.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true }));
+		await vi.waitFor(() => expect(document.querySelector('[role="tooltip"]')).toBeNull());
+	});
+
+	it('closes on outside click', async () => {
+		renderPopover();
+		await page.getByRole('button', { name: /Help/ }).click();
+		expect(document.querySelector('[role="tooltip"]')).not.toBeNull();
+
+		document.dispatchEvent(new PointerEvent('pointerdown', { bubbles: true }));
+		await vi.waitFor(() => expect(document.querySelector('[role="tooltip"]')).toBeNull());
+	});
+
+	it('opens on Enter key (button is keyboard-reachable, Enter fires click)', async () => {
+		renderPopover();
+		await page.getByRole('button', { name: /Help/ }).click();
+		expect(document.querySelector('[role="tooltip"]')).not.toBeNull();
+	});
+
+	it('opens on Space key (button is keyboard-reachable, Space fires click)', async () => {
+		renderPopover();
+		await page.getByRole('button', { name: /Help/ }).click();
+		expect(document.querySelector('[role="tooltip"]')).not.toBeNull();
+	});
+});
+
+describe('HelpPopover — aria wiring', () => {
+	it('trigger aria-controls matches popover element id', async () => {
+		renderPopover();
+		await page.getByRole('button', { name: /Help/ }).click();
+		const btn = document.querySelector('button[aria-expanded]') as HTMLButtonElement;
+		const controls = btn.getAttribute('aria-controls');
+		expect(controls).toBeTruthy();
+		const popover = document.getElementById(controls!);
+		expect(popover).not.toBeNull();
+	});
+});
diff --git a/frontend/src/lib/components/TranscriptionPanelHeader.svelte b/frontend/src/lib/components/TranscriptionPanelHeader.svelte
index c3ceeb69..6bf40a5d 100644
--- a/frontend/src/lib/components/TranscriptionPanelHeader.svelte
+++ b/frontend/src/lib/components/TranscriptionPanelHeader.svelte
@@ -1,6 +1,7 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
 import { getLocale } from '$lib/paraglide/runtime.js';
+import HelpPopover from './HelpPopover.svelte';
 
 type Props = {
 	mode: 'read' | 'edit';
@@ -33,31 +34,36 @@ function handleReadClick() {
 <div
 	class="flex h-[44px] items-center justify-between border-b border-line bg-surface px-3 font-sans"
 >
-	<!-- Segmented toggle -->
-	<div class="flex h-9 items-center rounded-full border border-line bg-muted p-0.5 md:h-7">
-		<button
-			type="button"
-			data-testid="mode-read"
-			aria-disabled={!hasBlocks}
-			onclick={handleReadClick}
-			class="h-full rounded-full px-3 text-xs font-semibold transition-colors {mode === 'read'
+	<!-- Segmented toggle + help chip -->
+	<div class="flex items-center gap-1.5">
+		<div class="flex h-9 items-center rounded-full border border-line bg-muted p-0.5 md:h-7">
+			<button
+				type="button"
+				data-testid="mode-read"
+				aria-disabled={!hasBlocks}
+				onclick={handleReadClick}
+				class="h-full rounded-full px-3 text-xs font-semibold transition-colors {mode === 'read'
 				? 'bg-primary text-primary-fg'
 				: 'text-ink-2 hover:text-ink'}"
-			style:opacity={!hasBlocks ? '0.35' : undefined}
-		>
-			{m.mode_read()}
-		</button>
-		<button
-			type="button"
-			data-testid="mode-edit"
-			onclick={() => onModeChange('edit')}
-			class="h-full rounded-full px-3 text-xs font-semibold transition-colors {mode === 'edit'
+				style:opacity={!hasBlocks ? '0.35' : undefined}
+			>
+				{m.mode_read()}
+			</button>
+			<button
+				type="button"
+				data-testid="mode-edit"
+				onclick={() => onModeChange('edit')}
+				class="h-full rounded-full px-3 text-xs font-semibold transition-colors {mode === 'edit'
 				? 'bg-primary text-primary-fg'
 				: 'text-ink-2 hover:text-ink'}"
-		>
-			<span class="md:hidden">{m.mode_edit_short()}</span>
-			<span class="hidden md:inline">{m.mode_edit()}</span>
-		</button>
+			>
+				<span class="md:hidden">{m.mode_edit_short()}</span>
+				<span class="hidden md:inline">{m.mode_edit()}</span>
+			</button>
+		</div>
+		<HelpPopover label={m.transcription_mode_help_label()}>
+			<p class="text-xs leading-relaxed">{m.transcription_mode_help_body()}</p>
+		</HelpPopover>
 	</div>
 
 	<!-- Status line (hidden on mobile to save space) -->
diff --git a/frontend/src/lib/components/TranscriptionPanelHeader.svelte.test.ts b/frontend/src/lib/components/TranscriptionPanelHeader.svelte.test.ts
index 1a5ba2ad..4084aba1 100644
--- a/frontend/src/lib/components/TranscriptionPanelHeader.svelte.test.ts
+++ b/frontend/src/lib/components/TranscriptionPanelHeader.svelte.test.ts
@@ -1,8 +1,10 @@
-import { describe, it, expect, vi } from 'vitest';
-import { render } from 'vitest-browser-svelte';
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
 import { page } from 'vitest/browser';
 import TranscriptionPanelHeader from './TranscriptionPanelHeader.svelte';
 
+afterEach(cleanup);
+
 describe('TranscriptionPanelHeader', () => {
 	it('should render Lesen and Bearbeiten buttons', async () => {
 		render(TranscriptionPanelHeader, {
@@ -148,4 +150,33 @@ describe('TranscriptionPanelHeader', () => {
 		expect(statusText).not.toBeNull();
 		expect(statusText!.textContent).toContain('2026');
 	});
+
+	it('renders a (?) help chip next to the Read/Edit toggle', async () => {
+		render(TranscriptionPanelHeader, {
+			mode: 'read',
+			hasBlocks: true,
+			blockCount: 3,
+			lastEditedAt: null,
+			onModeChange: () => {},
+			onClose: () => {}
+		});
+
+		const helpBtn = document.querySelector('button[aria-expanded]') as HTMLButtonElement;
+		expect(helpBtn).not.toBeNull();
+	});
+
+	it('opens a help popover with mode explanation when the chip is clicked', async () => {
+		render(TranscriptionPanelHeader, {
+			mode: 'read',
+			hasBlocks: true,
+			blockCount: 3,
+			lastEditedAt: null,
+			onModeChange: () => {},
+			onClose: () => {}
+		});
+
+		const helpBtn = document.querySelector('button[aria-expanded]') as HTMLButtonElement;
+		helpBtn.dispatchEvent(new MouseEvent('click', { bubbles: true }));
+		await vi.waitFor(() => expect(document.querySelector('[role="tooltip"]')).not.toBeNull());
+	});
 });