diff --git a/packages/gitbook/src/components/AI/references.ts b/packages/gitbook/src/components/AI/references.ts
index d649b0611..76b162ff9 100644
--- a/packages/gitbook/src/components/AI/references.ts
+++ b/packages/gitbook/src/components/AI/references.ts
@@ -19,7 +19,13 @@ export type PageReference = BaseAIChatReference & {
     href?: string;
 };
 
-export type AIChatReference = CodeBlockReference | PageReference;
+export type TextReference = BaseAIChatReference & {
+    type: 'text';
+    /** The selected text content. */
+    content: string;
+};
+
+export type AIChatReference = CodeBlockReference | PageReference | TextReference;
 
 /**
  * Serialize the staged references into a preamble prepended to the user's message,
@@ -42,6 +48,11 @@ export function serializeReferences(refs: AIChatReference[]): string {
         sections.push(serializeCodeBlockReferences(codeRefs));
     }
 
+    const textRefs = refs.filter((ref): ref is TextReference => ref.type === 'text');
+    if (textRefs.length > 0) {
+        sections.push(serializeTextReferences(textRefs));
+    }
+
     if (sections.length === 0) {
         return '';
     }
@@ -66,6 +77,19 @@ function serializeCodeBlockReferences(refs: CodeBlockReference[]): string {
     return `The user is referring to the following code block${plural ? 's' : ''} from the page they are reading. Answer their question about ${plural ? 'them' : 'it'}:\n\n${blocks}`;
 }
 
+function serializeTextReferences(refs: TextReference[]): string {
+    const plural = refs.length > 1;
+    const blocks = refs.map((ref) => quoteText(ref.content)).join('\n\n');
+    return `The user is referring to the following excerpt${plural ? 's' : ''} from the page they are reading. Answer their question about ${plural ? 'them' : 'it'}:\n\n${blocks}`;
+}
+
+function quoteText(content: string): string {
+    return content
+        .split('\n')
+        .map((line) => `> ${line}`)
+        .join('\n');
+}
+
 function buildCodeBlockFence(ref: CodeBlockReference): string {
     const { label, content, syntax } = ref;
     let max = 2;
diff --git a/packages/gitbook/src/components/AIChat/AIChatReferenceChips.tsx b/packages/gitbook/src/components/AIChat/AIChatReferenceChips.tsx
index daa91886a..d7db9df2f 100644
--- a/packages/gitbook/src/components/AIChat/AIChatReferenceChips.tsx
+++ b/packages/gitbook/src/components/AIChat/AIChatReferenceChips.tsx
@@ -33,7 +33,7 @@ export function AIChatReferenceChips(props: {
                                 ref.type === 'code-block' && 'font-mono'
                             )}
                         >
-                            {ref.label}
+                            {ref.type === 'text' ? ref.content : ref.label}
                         </span>
                     </>
                 );
@@ -55,6 +55,10 @@ export function AIChatReferenceChips(props: {
                             >
                                 {content}
                             </Link>
+                        ) : ref.type === 'text' ? (
+                            // A text selection has no persistent DOM anchor to navigate to, so the
+                            // excerpt is shown as plain (non-interactive) content.
+                            <span className={triggerClassName}>{content}</span>
                         ) : (
                             <button
                                 type="button"
@@ -94,6 +98,8 @@ function getReferenceIcon(ref: AIChatReference): IconName {
             return 'code';
         case 'page':
             return 'memo';
+        case 'text':
+            return 'quote-left';
         default:
             assertNever(ref);
     }
diff --git a/packages/gitbook/src/components/AIChat/AskAITextSelection/AskAITextSelection.tsx b/packages/gitbook/src/components/AIChat/AskAITextSelection/AskAITextSelection.tsx
new file mode 100644
index 000000000..94056b6ee
--- /dev/null
+++ b/packages/gitbook/src/components/AIChat/AskAITextSelection/AskAITextSelection.tsx
@@ -0,0 +1,129 @@
+'use client';
+
+import { CustomizationAIMode } from '@gitbook/api';
+import fnv1a from '@sindresorhus/fnv1a';
+import { AnimatePresence, motion } from 'motion/react';
+import * as React from 'react';
+import { createPortal } from 'react-dom';
+
+import { useAIChatController, useAIConfig } from '@/components/AI';
+import { useIsMobile } from '@/components/hooks/useIsMobile';
+import { useIsMounted } from '@/components/hooks/useIsMounted';
+import { Button } from '@/components/primitives';
+import { t, useLanguage } from '@/intl/client';
+
+import { AIChatIcon } from '../AIChatIcon';
+import { useStableTextSelection } from './useStableTextSelection';
+
+/** Gap between the selection and the button. */
+const GAP = 8;
+/** Minimum distance to the viewport edges. */
+const MARGIN = 8;
+
+/**
+ * Floating "Ask" button anchored above a text selection. Clicking it stages the selection as a
+ * reference and opens the AI chat. Only rendered in Assistant mode, on non-touch devices.
+ */
+export function AskAITextSelection() {
+    const config = useAIConfig();
+    const language = useLanguage();
+    const chatController = useAIChatController();
+    const isMobile = useIsMobile();
+    const isMounted = useIsMounted();
+
+    const enabled = config.aiMode === CustomizationAIMode.Assistant && !isMobile;
+
+    const toolbarRef = React.useRef<HTMLDivElement>(null);
+    const { selection, clear } = useStableTextSelection({
+        rootSelector: '[data-content-ref-root]',
+        enabled,
+        ignoreRef: toolbarRef,
+    });
+
+    const [coords, setCoords] = React.useState<{ top: number; left: number } | null>(null);
+
+    // Position once the button has been measured, so it can be centered and clamped to the viewport.
+    React.useLayoutEffect(() => {
+        if (!selection) {
+            return;
+        }
+        const el = toolbarRef.current;
+        if (!el) {
+            return;
+        }
+
+        const width = el.offsetWidth;
+        const height = el.offsetHeight;
+        const { anchor } = selection;
+
+        let top = anchor.top - GAP - height;
+        if (top < MARGIN) {
+            // Not enough room above the selection: drop below it.
+            top = anchor.bottom + GAP;
+        }
+        top = Math.min(top, window.innerHeight - height - MARGIN);
+
+        const left = Math.min(
+            Math.max(anchor.centerX - width / 2, MARGIN),
+            window.innerWidth - width - MARGIN
+        );
+
+        setCoords({ top, left });
+    }, [selection]);
+
+    const onClick = () => {
+        if (!selection) {
+            return;
+        }
+        const content = selection.text;
+        if (!content.trim()) {
+            return;
+        }
+
+        chatController.addReference({
+            type: 'text',
+            id: `text-${fnv1a(content, { size: 32 })}`,
+            content,
+        });
+        chatController.open();
+        chatController.focus();
+        clear();
+    };
+
+    if (!enabled || !isMounted) {
+        return null;
+    }
+
+    return createPortal(
+        <AnimatePresence>
+            {selection ? (
+                <motion.div
+                    ref={toolbarRef}
+                    initial={{ opacity: 0, scale: 0.92 }}
+                    animate={{ opacity: coords ? 1 : 0, scale: 1 }}
+                    exit={{ opacity: 0, scale: 0.92 }}
+                    transition={{ duration: 0.12, ease: 'easeOut' }}
+                    style={{
+                        position: 'fixed',
+                        top: coords?.top ?? 0,
+                        left: coords?.left ?? 0,
+                        zIndex: 40,
+                    }}
+                    // Keep the selection alive: prevent the button from stealing focus on click.
+                    onMouseDown={(event) => event.preventDefault()}
+                >
+                    <Button
+                        size="small"
+                        variant="primary"
+                        icon={<AIChatIcon state="default" trademark={config.trademark} />}
+                        onClick={onClick}
+                        className="shadow-sm"
+                    >
+                        {t(language, 'ask')}
+                    </Button>
+                </motion.div>
+            ) : null}
+        </AnimatePresence>,
+        document.body
+    );
+}
diff --git a/packages/gitbook/src/components/AIChat/AskAITextSelection/index.ts b/packages/gitbook/src/components/AIChat/AskAITextSelection/index.ts
new file mode 100644
index 000000000..5e6f83c85
--- /dev/null
+++ b/packages/gitbook/src/components/AIChat/AskAITextSelection/index.ts
@@ -0,0 +1 @@
+export * from './AskAITextSelection';
diff --git a/packages/gitbook/src/components/AIChat/AskAITextSelection/useStableTextSelection.ts b/packages/gitbook/src/components/AIChat/AskAITextSelection/useStableTextSelection.ts
new file mode 100644
index 000000000..ae0e92f3c
--- /dev/null
+++ b/packages/gitbook/src/components/AIChat/AskAITextSelection/useStableTextSelection.ts
@@ -0,0 +1,202 @@
+'use client';
+
+import * as React from 'react';
+
+type SelectionAnchor = {
+    top: number;
+    bottom: number;
+    centerX: number;
+};
+
+export type StableTextSelection = {
+    anchor: SelectionAnchor;
+    text: string;
+};
+
+type Options = {
+    /** Selector of the content root; both selection endpoints must be inside it. */
+    rootSelector: string;
+    enabled: boolean;
+    /** Pointer events inside this element are ignored, so clicking the UI keeps the selection. */
+    ignoreRef: React.RefObject<HTMLElement | null>;
+};
+
+const KEYBOARD_DEBOUNCE_MS = 250;
+const SCROLL_SETTLE_MS = 200;
+// Coalesces the rapid down/up bursts of a double/triple-click into a single, non-flashing show.
+const POINTER_SETTLE_MS = 120;
+
+/**
+ * Track a stable text selection within `rootSelector`, debounced so the floating UI it powers
+ * doesn't flicker mid-gesture. The selection is dropped on collapse, window blur, scroll, and
+ * when a new gesture starts.
+ */
+export function useStableTextSelection(options: Options): {
+    selection: StableTextSelection | null;
+    clear: () => void;
+} {
+    const { rootSelector, enabled, ignoreRef } = options;
+    const [selection, setSelection] = React.useState<StableTextSelection | null>(null);
+
+    const clear = React.useCallback(() => {
+        window.getSelection()?.removeAllRanges();
+        setSelection(null);
+    }, []);
+
+    React.useEffect(() => {
+        if (!enabled) {
+            setSelection(null);
+            return;
+        }
+
+        let pointerDown = false;
+        let keyboardTimer: ReturnType<typeof setTimeout> | null = null;
+        let scrollTimer: ReturnType<typeof setTimeout> | null = null;
+        let finalizeTimer: ReturnType<typeof setTimeout> | null = null;
+
+        const clearKeyboardTimer = () => {
+            if (keyboardTimer) {
+                clearTimeout(keyboardTimer);
+                keyboardTimer = null;
+            }
+        };
+
+        const clearFinalizeTimer = () => {
+            if (finalizeTimer) {
+                clearTimeout(finalizeTimer);
+                finalizeTimer = null;
+            }
+        };
+
+        const finalize = () => {
+            // A new gesture started; it will reschedule its own finalize.
+            if (pointerDown) {
+                return;
+            }
+            setSelection(readStableSelection(rootSelector));
+        };
+
+        const schedulePointerFinalize = () => {
+            clearKeyboardTimer();
+            clearFinalizeTimer();
+            finalizeTimer = setTimeout(() => {
+                finalizeTimer = null;
+                finalize();
+            }, POINTER_SETTLE_MS);
+        };
+
+        const isIgnored = (target: EventTarget | null) =>
+            target instanceof Node && !!ignoreRef.current?.contains(target);
+
+        const onSelectionChange = () => {
+            const sel = window.getSelection();
+            if (!sel || sel.isCollapsed || sel.rangeCount === 0 || !sel.toString().trim()) {
+                clearKeyboardTimer();
+                setSelection(null);
+                return;
+            }
+            // Mid-drag, or a pointer finalize is already queued: let the gesture settle first.
+            if (pointerDown || finalizeTimer) {
+                return;
+            }
+            clearKeyboardTimer();
+            keyboardTimer = setTimeout(finalize, KEYBOARD_DEBOUNCE_MS);
+        };
+
+        const onPointerDown = (event: PointerEvent) => {
+            if (isIgnored(event.target)) {
+                return;
+            }
+            // New gesture: hide and cancel a pending show so it can't fire mid double-click.
+            pointerDown = true;
+            clearFinalizeTimer();
+            setSelection(null);
+        };
+
+        const onPointerUp = (event: PointerEvent) => {
+            if (isIgnored(event.target)) {
+                return;
+            }
+            pointerDown = false;
+            schedulePointerFinalize();
+        };
+
+        // pointercancel replaces pointerup when a gesture is interrupted (OS gesture, scroll handoff).
+        const onPointerCancel = () => {
+            pointerDown = false;
+            schedulePointerFinalize();
+        };
+
+        const onScroll = () => {
+            setSelection(null);
+            if (scrollTimer) {
+                clearTimeout(scrollTimer);
+            }
+            scrollTimer = setTimeout(() => {
+                if (!pointerDown) {
+                    finalize();
+                }
+            }, SCROLL_SETTLE_MS);
+        };
+
+        const onWindowBlur = () => {
+            clearKeyboardTimer();
+            setSelection(null);
+        };
+
+        document.addEventListener('selectionchange', onSelectionChange);
+        document.addEventListener('pointerdown', onPointerDown, true);
+        document.addEventListener('pointerup', onPointerUp, true);
+        document.addEventListener('pointercancel', onPointerCancel, true);
+        window.addEventListener('scroll', onScroll, true);
+        window.addEventListener('blur', onWindowBlur);
+
+        return () => {
+            document.removeEventListener('selectionchange', onSelectionChange);
+            document.removeEventListener('pointerdown', onPointerDown, true);
+            document.removeEventListener('pointerup', onPointerUp, true);
+            document.removeEventListener('pointercancel', onPointerCancel, true);
+            window.removeEventListener('scroll', onScroll, true);
+            window.removeEventListener('blur', onWindowBlur);
+            clearKeyboardTimer();
+            clearFinalizeTimer();
+            if (scrollTimer) {
+                clearTimeout(scrollTimer);
+            }
+        };
+    }, [enabled, rootSelector, ignoreRef]);
+
+    return { selection, clear };
+}
+
+function readStableSelection(rootSelector: string): StableTextSelection | null {
+    const sel = window.getSelection();
+    if (!sel || sel.isCollapsed || sel.rangeCount === 0) {
+        return null;
+    }
+
+    const text = sel.toString().trim();
+    if (!text) {
+        return null;
+    }
+
+    const root = document.querySelector(rootSelector);
+    if (!root || !root.contains(sel.anchorNode) || !root.contains(sel.focusNode)) {
+        return null;
+    }
+
+    const anchor = getSelectionAnchor(sel);
+    return anchor ? { anchor, text } : null;
+}
+
+/** Box centered above the whole selection, or null if it has no size or is scrolled out of view. */
+function getSelectionAnchor(sel: Selection): SelectionAnchor | null {
+    const rect = sel.getRangeAt(0).getBoundingClientRect();
+    if (!rect.width && !rect.height) {
+        return null;
+    }
+    if (rect.bottom < 0 || rect.top > window.innerHeight) {
+        return null;
+    }
+    return { top: rect.top, bottom: rect.bottom, centerX: rect.left + rect.width / 2 };
+}
diff --git a/packages/gitbook/src/components/AIChat/index.ts b/packages/gitbook/src/components/AIChat/index.ts
index 12eaa899e..57307673a 100644
--- a/packages/gitbook/src/components/AIChat/index.ts
+++ b/packages/gitbook/src/components/AIChat/index.ts
@@ -3,3 +3,4 @@ export * from './AIChatButton';
 export * from './AIChatIcon';
 export * from './AIResponseFeedback';
 export * from './AIChatControlButton';
+export * from './AskAITextSelection';
diff --git a/packages/gitbook/src/components/PageBody/PageBody.tsx b/packages/gitbook/src/components/PageBody/PageBody.tsx
index a24d73140..adb97b94d 100644
--- a/packages/gitbook/src/components/PageBody/PageBody.tsx
+++ b/packages/gitbook/src/components/PageBody/PageBody.tsx
@@ -106,18 +106,20 @@ export async function PageBody(props: {
                         fallback={<DocumentViewSkeleton document={document} blockStyle="" />}
                     >
                         <SuspenseLoadedHint />
-                        <DocumentView
-                            document={document}
-                            style="flex flex-col [&>*+*]:mt-5"
-                            context={{
-                                mode: 'default',
-                                contentContext: {
-                                    ...context,
-                                    page,
-                                },
-                                withLinkPreviews,
-                            }}
-                        />
+                        <div className="contents" data-content-ref-root="">
+                            <DocumentView
+                                document={document}
+                                style="flex flex-col [&>*+*]:mt-5"
+                                context={{
+                                    mode: 'default',
+                                    contentContext: {
+                                        ...context,
+                                        page,
+                                    },
+                                    withLinkPreviews,
+                                }}
+                            />
+                        </div>
                     </OptionalSuspense>
                 ) : (
                     <PageBodyBlankslate page={page} context={context} />
diff --git a/packages/gitbook/src/components/SpaceLayout/SpaceLayout.tsx b/packages/gitbook/src/components/SpaceLayout/SpaceLayout.tsx
index 20673d49f..9b0a26133 100644
--- a/packages/gitbook/src/components/SpaceLayout/SpaceLayout.tsx
+++ b/packages/gitbook/src/components/SpaceLayout/SpaceLayout.tsx
@@ -14,7 +14,7 @@ import { GITBOOK_APP_URL } from '@/lib/env';
 import { tcls } from '@/lib/tailwind';
 import { AIChatProvider } from '../AI';
 import type { RenderAIMessageOptions } from '../AI';
-import { AIChat } from '../AIChat';
+import { AIChat, AskAITextSelection } from '../AIChat';
 import { AdaptiveVisitorContextProvider } from '../Adaptive';
 import { Announcement } from '../Announcement';
 import { SpacesDropdown, TranslationsDropdown } from '../Header/SpacesDropdown';
@@ -127,7 +127,12 @@ export function SpaceLayout(props: SpaceLayoutProps) {
             <Announcement context={context} />
             <Header withTopHeader={withTopHeader} variants={variants} context={context} />
             <NavigationLoader />
-            {customization.ai?.mode === CustomizationAIMode.Assistant ? <AIChat /> : null}
+            {customization.ai?.mode === CustomizationAIMode.Assistant ? (
+                <>
+                    <AIChat />
+                    <AskAITextSelection />
+                </>
+            ) : null}
 
             {/* Chat panel shifts content left when open */}
             <div className="motion-safe:transition-all motion-safe:duration-300 lg:chat-open:mr-80 xl:chat-open:mr-96">