diff --git a/src/components/DarkModeToggle.astro b/src/components/DarkModeToggle.astro
index 29d2979..1e4954f 100644
--- a/src/components/DarkModeToggle.astro
+++ b/src/components/DarkModeToggle.astro
@@ -1,16 +1,30 @@
 ---
-// DarkModeToggle component - toggles between light and dark mode
+// DarkModeToggle component - cycles between auto / light / dark
 ---
 
 <button
   id="darkModeToggle"
   type="button"
   class="flex items-center justify-center w-8 h-8 rounded-lg cursor-pointer text-neutral-600 dark:text-neutral-300 hover:text-neutral-900 dark:hover:text-white hover:bg-neutral-100 dark:hover:bg-neutral-800 transition-colors"
-  aria-label="Toggle dark mode"
+  aria-label="Changer le thème"
 >
+  <!-- Auto icon (system preference) -->
   <svg
-    class="w-5 h-5 dark:hidden"
-    id="sunIcon"
+    class="w-5 h-5 hidden"
+    data-theme-icon="auto"
+    fill="none"
+    stroke-linecap="round"
+    stroke-linejoin="round"
+    stroke-width="2"
+    viewBox="0 0 24 24"
+    stroke="currentColor"
+  >
+    <path d="M9.75 17L9 20l-1 1h8l-1-1-.75-3M3 13h18M5 17h14a2 2 0 002-2V5a2 2 0 00-2-2H5a2 2 0 00-2 2v10a2 2 0 002 2z"></path>
+  </svg>
+  <!-- Light icon (sun) -->
+  <svg
+    class="w-5 h-5 hidden"
+    data-theme-icon="light"
     fill="none"
     stroke-linecap="round"
     stroke-linejoin="round"
@@ -22,9 +36,10 @@
       d="M12 3v1m0 16v1m9-9h-1M4 12H3m15.364 6.364l-.707-.707M6.343 6.343l-.707-.707m12.728 0l-.707.707M6.343 17.657l-.707.707M16 12a4 4 0 11-8 0 4 4 0 018 0z"
     ></path>
   </svg>
+  <!-- Dark icon (moon) -->
   <svg
-    class="hidden w-5 h-5 dark:block"
-    id="moonIcon"
+    class="w-5 h-5 hidden"
+    data-theme-icon="dark"
     fill="none"
     stroke-linecap="round"
     stroke-linejoin="round"
@@ -39,17 +54,62 @@
 </button>
 
 <script>
-  function setupDarkModeToggle() {
-    const toggle = document.getElementById('darkModeToggle');
+  function getThemePreference(): 'auto' | 'light' | 'dark' {
+    const stored = localStorage.getItem('theme');
+    if (stored === 'light' || stored === 'dark') return stored;
+    return 'auto';
+  }
 
-    toggle?.addEventListener('click', () => {
-      document.documentElement.classList.toggle('dark');
-      const isDark = document.documentElement.classList.contains('dark');
-      localStorage.setItem('theme', isDark ? 'dark' : 'light');
+  function getEffectiveDark(preference: 'auto' | 'light' | 'dark'): boolean {
+    if (preference === 'dark') return true;
+    if (preference === 'light') return false;
+    return window.matchMedia('(prefers-color-scheme: dark)').matches;
+  }
+
+  function applyTheme(preference: 'auto' | 'light' | 'dark') {
+    const isDark = getEffectiveDark(preference);
+    document.documentElement.classList.toggle('dark', isDark);
+    updateIcon(preference);
+    updateAriaLabel(preference);
+  }
+
+  function updateIcon(preference: 'auto' | 'light' | 'dark') {
+    document.querySelectorAll<HTMLElement>('[data-theme-icon]').forEach(icon => {
+      icon.classList.toggle('hidden', icon.dataset.themeIcon !== preference);
+    });
+  }
+
+  function updateAriaLabel(preference: 'auto' | 'light' | 'dark') {
+    const toggle = document.getElementById('darkModeToggle');
+    const labels = { auto: 'Thème : automatique', light: 'Thème : clair', dark: 'Thème : sombre' };
+    toggle?.setAttribute('aria-label', labels[preference]);
+  }
+
+  const cycle: Record<string, 'light' | 'dark' | 'auto'> = { auto: 'light', light: 'dark', dark: 'auto' };
+
+  function setupDarkModeToggle() {
+    const toggle = document.getElementById('darkModeToggle');
+    const preference = getThemePreference();
+    applyTheme(preference);
+
+    toggle?.addEventListener('click', () => {
+      const current = getThemePreference();
+      const next = cycle[current];
+      if (next === 'auto') {
+        localStorage.removeItem('theme');
+      } else {
+        localStorage.setItem('theme', next);
+      }
+      applyTheme(next);
+    });
+
+    window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
+      if (getThemePreference() === 'auto') {
+        applyTheme('auto');
+      }
     });
   }
 
-  // Run on page load and on Astro navigation
   setupDarkModeToggle();
   document.addEventListener('astro:after-swap', setupDarkModeToggle);
-</script>
\ No newline at end of file
+</script>
diff --git a/src/layouts/main.astro b/src/layouts/main.astro
index e61bef1..05b6092 100644
--- a/src/layouts/main.astro
+++ b/src/layouts/main.astro
@@ -15,7 +15,8 @@ const { title } = Astro.props;
     <!-- Used to add dark mode right away, adding here prevents any flicker -->
     <script is:inline>
       if (typeof Storage !== 'undefined') {
-        if (localStorage.getItem('theme') === 'dark') {
+        var theme = localStorage.getItem('theme');
+        if (theme === 'dark' || (!theme && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
           document.documentElement.classList.add('dark')
         }
       }