diff --git a/src/App.tsx b/src/App.tsx
index c693b3c..74437b1 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,4 +1,4 @@
-import { useState } from "react";
+import { useCallback, useEffect, useState } from "react";
 import type { Editor as TiptapEditor } from "@tiptap/react";
 import { Sidebar } from "./components/Sidebar";
 import { Dock } from "./components/Dock";
@@ -6,6 +6,7 @@ import { Icon } from "./components/Icon";
 import { Editor } from "./editor/Editor";
 import { FloatingToolbar } from "./editor/FloatingToolbar";
 import { useBook } from "./store/useBook";
+import { chooseSavePath, openBook, writeBook } from "./project";
 
 function App() {
   const [dock, setDock] = useState(true);
@@ -14,20 +15,59 @@ function App() {
   const author = useBook((s) => s.book.metadata.author);
   const chapters = useBook((s) => s.book.chapters);
   const activeChapterId = useBook((s) => s.activeChapterId);
+  const dirty = useBook((s) => s.dirty);
   const setChapterContent = useBook((s) => s.setChapterContent);
   const setChapterTitle = useBook((s) => s.setChapterTitle);
+  const replaceBook = useBook((s) => s.replaceBook);
+  const markSaved = useBook((s) => s.markSaved);
 
   const idx = chapters.findIndex((c) => c.id === activeChapterId);
   const chapter = chapters[idx];
 
+  const handleSave = useCallback(async () => {
+    const { book, path } = useBook.getState();
+    const target = path ?? (await chooseSavePath(book));
+    if (!target) return;
+    await writeBook(book, target);
+    markSaved(target);
+  }, [markSaved]);
+
+  const handleOpen = useCallback(async () => {
+    const result = await openBook();
+    if (result) replaceBook(result.book, result.path);
+  }, [replaceBook]);
+
+  useEffect(() => {
+    const onKey = (e: KeyboardEvent) => {
+      const mod = e.metaKey || e.ctrlKey;
+      if (mod && e.key.toLowerCase() === "s") {
+        e.preventDefault();
+        handleSave();
+      }
+      if (mod && e.key.toLowerCase() === "o") {
+        e.preventDefault();
+        handleOpen();
+      }
+    };
+    window.addEventListener("keydown", onKey);
+    return () => window.removeEventListener("keydown", onKey);
+  }, [handleSave, handleOpen]);
+
   return (
     <div className="app">
       <header className="titlebar" data-tauri-drag-region>
         <span className="doc-title">
           {title || "Untitled"}
           {author ? ` — ${author}` : ""}
+          {dirty && <span className="dirty-dot" />}
         </span>
         <div className="actions">
+          <button className="icon-btn" onClick={handleOpen} title="Open (⌘O)">
+            <Icon d="M3 7l1.7-2.5h4.6L11 7h8a1 1 0 0 1 1 1v10a1 1 0 0 1-1 1H4a1 1 0 0 1-1-1z" />
+          </button>
+          <button className="icon-btn" onClick={handleSave} title="Save (⌘S)">
+            <Icon d="M12 4v10m0 0l-3.5-3.5M12 14l3.5-3.5M5 19h14" />
+          </button>
           <button className="icon-btn" data-on={dock} onClick={() => setDock(!dock)} title="Toggle preview">
             <Icon d="M3 4.5h18v15H3zM14 4.5v15" />
           </button>
diff --git a/src/project.ts b/src/project.ts
new file mode 100644
index 0000000..54c8353
--- /dev/null
+++ b/src/project.ts
@@ -0,0 +1,20 @@
+import { save, open } from "@tauri-apps/plugin-dialog";
+import { invoke } from "@tauri-apps/api/core";
+import type { Book } from "./model/book";
+
+const FILTERS = [{ name: "margin book", extensions: ["margin"] }];
+
+export async function chooseSavePath(book: Book): Promise<string | null> {
+  return save({ filters: FILTERS, defaultPath: `${book.metadata.title || "Untitled"}.margin` });
+}
+
+export async function writeBook(book: Book, path: string): Promise<void> {
+  await invoke("write_file", { path, contents: JSON.stringify(book, null, 2) });
+}
+
+export async function openBook(): Promise<{ book: Book; path: string } | null> {
+  const selected = await open({ filters: FILTERS, multiple: false, directory: false });
+  if (typeof selected !== "string") return null;
+  const contents = await invoke<string>("read_file", { path: selected });
+  return { book: JSON.parse(contents) as Book, path: selected };
+}
diff --git a/src/store/useBook.ts b/src/store/useBook.ts
index 033b75e..a8fbf2b 100644
--- a/src/store/useBook.ts
+++ b/src/store/useBook.ts
@@ -5,11 +5,14 @@ import { type Book, createChapter, starterBook } from "../model/book";
 interface BookState {
   book: Book;
   activeChapterId: string;
+  path: string | null;
   dirty: boolean;
   setActiveChapter: (id: string) => void;
   setChapterContent: (id: string, content: JSONContent) => void;
   setChapterTitle: (id: string, title: string) => void;
   addChapter: () => void;
+  replaceBook: (book: Book, path: string) => void;
+  markSaved: (path: string) => void;
 }
 
 export const useBook = create<BookState>((set) => {
@@ -17,6 +20,7 @@ export const useBook = create<BookState>((set) => {
   return {
     book,
     activeChapterId: book.chapters[0].id,
+    path: null,
     dirty: false,
     setActiveChapter: (id) => set({ activeChapterId: id }),
     setChapterContent: (id, content) =>
@@ -44,5 +48,8 @@ export const useBook = create<BookState>((set) => {
           book: { ...s.book, chapters: [...s.book.chapters, chapter] },
         };
       }),
+    replaceBook: (book, path) =>
+      set({ book, activeChapterId: book.chapters[0]?.id ?? "", path, dirty: false }),
+    markSaved: (path) => set({ path, dirty: false }),
   };
 });
diff --git a/src/styles/app.css b/src/styles/app.css
index 0a5bad2..9b82d16 100644
--- a/src/styles/app.css
+++ b/src/styles/app.css
@@ -82,6 +82,16 @@ button {
   color: var(--accent);
 }
 
+.dirty-dot {
+  display: inline-block;
+  width: 5px;
+  height: 5px;
+  margin-left: 8px;
+  border-radius: 50%;
+  background: var(--accent);
+  vertical-align: middle;
+}
+
 .body {
   flex: 1;
   display: flex;