diff --git a/next.config.mjs b/next.config.mjs
index 1a67b9f..11f2e90 100644
--- a/next.config.mjs
+++ b/next.config.mjs
@@ -1,6 +1,9 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   output: 'standalone',
+  experimental: {
+    globalNotFound: true,
+  },
   turbopack: {
     root: process.cwd(),
   },
diff --git a/src/app/global-not-found.module.css b/src/app/global-not-found.module.css
new file mode 100644
index 0000000..ea401d7
--- /dev/null
+++ b/src/app/global-not-found.module.css
@@ -0,0 +1,137 @@
+.page {
+  display: grid;
+  min-height: 100svh;
+  padding: var(--space-6) var(--layout-page-gutter);
+  place-items: center;
+  overflow: hidden;
+  background: var(--bg-page);
+  color: var(--text-primary);
+}
+
+.content {
+  display: flex;
+  width: min(100%, 36rem);
+  align-items: center;
+  flex-direction: column;
+  text-align: center;
+}
+
+.persian {
+  display: none;
+}
+
+:global(html[lang='fa']) .english {
+  display: none;
+}
+
+:global(html[lang='fa']) .persian {
+  display: flex;
+}
+
+.code {
+  color: color-mix(in srgb, var(--accent-default) 38%, var(--bg-page));
+  font-size: clamp(6rem, 22vw, 12rem);
+  font-weight: 850;
+  letter-spacing: -0.08em;
+  line-height: 0.82;
+  user-select: none;
+}
+
+:global(html[dir='rtl']) .code {
+  letter-spacing: 0;
+}
+
+.divider {
+  width: 3rem;
+  height: 0.2rem;
+  margin-block: var(--space-7) var(--space-5);
+  border-radius: var(--radius-pill);
+  background: var(--accent-default);
+}
+
+.content h1 {
+  max-width: 18ch;
+  color: var(--text-primary);
+  font-size: clamp(2rem, 5vw, 3rem);
+  font-weight: 780;
+  letter-spacing: -0.04em;
+  line-height: 1.12;
+  text-wrap: balance;
+}
+
+:global(html[dir='rtl']) .content h1 {
+  letter-spacing: 0;
+}
+
+.description {
+  max-width: 34rem;
+  margin-top: var(--space-4);
+  color: var(--text-secondary);
+  font-size: var(--font-size-body-large);
+  line-height: var(--line-height-body-large);
+  text-wrap: pretty;
+}
+
+.homeLink {
+  display: inline-flex;
+  min-height: var(--size-button-height);
+  align-items: center;
+  justify-content: center;
+  gap: var(--space-2);
+  margin-top: var(--space-7);
+  padding-inline: var(--space-5);
+  border: 1px solid transparent;
+  border-radius: var(--radius-pill);
+  background: var(--action-primary-bg);
+  color: var(--action-primary-fg);
+  font-size: var(--font-size-button);
+  font-weight: 700;
+  line-height: var(--line-height-button);
+  transition:
+    background-color var(--motion-duration-fast) ease,
+    box-shadow var(--motion-duration-fast) ease,
+    transform var(--motion-duration-fast) var(--motion-ease-out);
+}
+
+.homeLink svg {
+  width: var(--size-icon-md);
+  height: var(--size-icon-md);
+}
+
+.homeLink:active {
+  transform: scale(0.97);
+}
+
+@media (hover: hover) and (pointer: fine) {
+  .homeLink:hover {
+    background: var(--action-primary-hover);
+    box-shadow: 0 0.25rem 0.75rem var(--shadow-color);
+    transform: translateY(-1px);
+  }
+}
+
+@media (max-width: 650px) {
+  .page {
+    padding-block: var(--space-5);
+  }
+
+  .divider {
+    margin-block: var(--space-6) var(--space-4);
+  }
+
+  .description {
+    font-size: var(--font-size-body-default);
+    line-height: var(--line-height-body-default);
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .homeLink {
+    transition: background-color 120ms ease, box-shadow 120ms ease;
+  }
+
+  .homeLink:hover,
+  .homeLink:active {
+    transform: none;
+  }
+}
diff --git a/src/app/global-not-found.tsx b/src/app/global-not-found.tsx
new file mode 100644
index 0000000..707768f
--- /dev/null
+++ b/src/app/global-not-found.tsx
@@ -0,0 +1,72 @@
+import type { Metadata } from 'next';
+import localFont from 'next/font/local';
+import Link from 'next/link';
+import { ArrowLeft, ArrowRight } from 'lucide-react';
+import { messagesByLocale, type Locale } from '@/i18n/content';
+import '@/styles/globals.css';
+import styles from './global-not-found.module.css';
+
+const themeAndLocaleScript = `
+  try {
+    const root = document.documentElement;
+    const isPersian = /^\\/fa(?:\\/|$)/.test(window.location.pathname);
+    root.lang = isPersian ? 'fa' : 'en';
+    root.dir = isPersian ? 'rtl' : 'ltr';
+    const savedTheme = localStorage.getItem('portfolio-theme');
+    root.dataset.theme = savedTheme === 'dark' ? 'dark' : 'light';
+  } catch {}
+`;
+
+const iranYekan = localFont({
+  src: '../../public/fonts/IRANYekanXVF.woff2',
+  variable: '--font-body',
+  weight: '100 1000',
+  style: 'normal',
+  display: 'swap',
+  preload: false,
+  fallback: ['-apple-system', 'BlinkMacSystemFont', 'Segoe UI', 'sans-serif'],
+});
+
+export const metadata: Metadata = {
+  title: '404 | Amirhossein Khalili',
+  description: 'The requested page could not be found.',
+};
+
+function NotFoundContent({ locale }: { locale: Locale }) {
+  const copy = messagesByLocale[locale].notFound;
+  const isRtl = locale === 'fa';
+
+  return (
+    <section
+      className={`${styles.content} ${locale === 'fa' ? styles.persian : styles.english}`}
+      lang={locale}
+      dir={isRtl ? 'rtl' : 'ltr'}
+      aria-labelledby={`not-found-title-${locale}`}
+    >
+      <p className={styles.code} aria-hidden="true">{copy.code}</p>
+      <span className={styles.divider} aria-hidden="true" />
+      <h1 id={`not-found-title-${locale}`}>{copy.title}</h1>
+      <p className={styles.description}>{copy.description}</p>
+      <Link href={isRtl ? '/fa' : '/'} className={styles.homeLink}>
+        {isRtl ? <ArrowRight aria-hidden="true" /> : <ArrowLeft aria-hidden="true" />}
+        <span>{copy.backHome}</span>
+      </Link>
+    </section>
+  );
+}
+
+export default function GlobalNotFound() {
+  return (
+    <html lang="en" dir="ltr" suppressHydrationWarning>
+      <head>
+        <script dangerouslySetInnerHTML={{ __html: themeAndLocaleScript }} />
+      </head>
+      <body className={iranYekan.variable}>
+        <main className={styles.page}>
+          <NotFoundContent locale="en" />
+          <NotFoundContent locale="fa" />
+        </main>
+      </body>
+    </html>
+  );
+}
diff --git a/src/i18n/content.ts b/src/i18n/content.ts
index 431a9c7..4e3dd23 100644
--- a/src/i18n/content.ts
+++ b/src/i18n/content.ts
@@ -9,6 +9,12 @@ export interface SiteMessages {
     description: string;
     keywords: string[];
   };
+  notFound: {
+    code: string;
+    title: string;
+    description: string;
+    backHome: string;
+  };
   loader: {
     signature: string;
     message: string;
@@ -146,6 +152,12 @@ export const messagesByLocale = {
         'Portfolio',
       ],
     },
+    notFound: {
+      code: '404',
+      title: 'This page isn’t here',
+      description: 'The address may have changed, or the page may no longer exist.',
+      backHome: 'Back to portfolio',
+    },
     loader: {
       signature: 'Amirhossein Khalili',
       message: 'Assembling the experience',
@@ -306,6 +318,12 @@ export const messagesByLocale = {
         'نمونه‌کار',
       ],
     },
+    notFound: {
+      code: '۴۰۴',
+      title: 'این صفحه پیدا نشد',
+      description: 'ممکن است نشانی صفحه تغییر کرده باشد یا دیگر در دسترس نباشد.',
+      backHome: 'بازگشت به نمونه‌کارها',
+    },
     loader: {
       signature: 'امیرحسین خلیلی',
       message: 'در حال آماده‌سازی صفحه',