diff --git a/crates/nuncio-tui/src/keybindings.rs b/crates/nuncio-tui/src/keybindings.rs
new file mode 100644
index 0000000..716593c
--- /dev/null
+++ b/crates/nuncio-tui/src/keybindings.rs
@@ -0,0 +1,124 @@
+//! Keyboard navigation, Vim-style shortcuts, and command dispatch engine.
+
+use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
+
+/// Action events mapped from terminal key inputs.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum UserAction {
+    /// Move selection down (j / Down).
+    MoveDown,
+    /// Move selection up (k / Up).
+    MoveUp,
+    /// Jump to top of list (gg).
+    JumpTop,
+    /// Jump to bottom of list (G).
+    JumpBottom,
+    /// Switch to next pane (Tab).
+    NextPane,
+    /// Switch to previous pane (BackTab).
+    PreviousPane,
+    /// Open search mode (/).
+    Search,
+    /// Compose new email message (c).
+    Compose,
+    /// Reply to selected message (r).
+    Reply,
+    /// Refresh / sync (s).
+    Sync,
+    /// Exit application or modal (q / Esc).
+    Quit,
+    /// Unmapped key action.
+    None,
+}
+
+/// Keybinding translation engine mapping crossterm input events to [`UserAction`].
+pub struct KeybindingEngine;
+
+impl KeybindingEngine {
+    /// Translate a crossterm [`KeyEvent`] into a [`UserAction`].
+    pub fn handle_key(key: KeyEvent) -> UserAction {
+        match (key.code, key.modifiers) {
+            (KeyCode::Char('q'), KeyModifiers::NONE) | (KeyCode::Esc, _) => UserAction::Quit,
+            (KeyCode::Char('j'), KeyModifiers::NONE) | (KeyCode::Down, _) => UserAction::MoveDown,
+            (KeyCode::Char('k'), KeyModifiers::NONE) | (KeyCode::Up, _) => UserAction::MoveUp,
+            (KeyCode::Char('g'), KeyModifiers::NONE) => UserAction::JumpTop,
+            (KeyCode::Char('G'), KeyModifiers::SHIFT) => UserAction::JumpBottom,
+            (KeyCode::Tab, KeyModifiers::NONE) => UserAction::NextPane,
+            (KeyCode::BackTab, _) => UserAction::PreviousPane,
+            (KeyCode::Char('/'), KeyModifiers::NONE) => UserAction::Search,
+            (KeyCode::Char('c'), KeyModifiers::NONE) => UserAction::Compose,
+            (KeyCode::Char('r'), KeyModifiers::NONE) => UserAction::Reply,
+            (KeyCode::Char('s'), KeyModifiers::NONE) => UserAction::Sync,
+            _ => UserAction::None,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn make_key(code: KeyCode, modifiers: KeyModifiers) -> KeyEvent {
+        KeyEvent::new(code, modifiers)
+    }
+
+    #[test]
+    fn translate_vim_motion_keys() {
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('j'), KeyModifiers::NONE)),
+            UserAction::MoveDown
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('k'), KeyModifiers::NONE)),
+            UserAction::MoveUp
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('g'), KeyModifiers::NONE)),
+            UserAction::JumpTop
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('G'), KeyModifiers::SHIFT)),
+            UserAction::JumpBottom
+        );
+    }
+
+    #[test]
+    fn translate_pane_navigation_and_quit() {
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Tab, KeyModifiers::NONE)),
+            UserAction::NextPane
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::BackTab, KeyModifiers::NONE)),
+            UserAction::PreviousPane
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('q'), KeyModifiers::NONE)),
+            UserAction::Quit
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Esc, KeyModifiers::NONE)),
+            UserAction::Quit
+        );
+    }
+
+    #[test]
+    fn translate_command_shortcuts() {
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('/'), KeyModifiers::NONE)),
+            UserAction::Search
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('c'), KeyModifiers::NONE)),
+            UserAction::Compose
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('r'), KeyModifiers::NONE)),
+            UserAction::Reply
+        );
+        assert_eq!(
+            KeybindingEngine::handle_key(make_key(KeyCode::Char('z'), KeyModifiers::NONE)),
+            UserAction::None
+        );
+    }
+}
diff --git a/crates/nuncio-tui/src/main.rs b/crates/nuncio-tui/src/main.rs
index eb79425..54da127 100644
--- a/crates/nuncio-tui/src/main.rs
+++ b/crates/nuncio-tui/src/main.rs
@@ -1,7 +1,9 @@
 //! Nuncio Terminal UI application entry point.
 
+mod keybindings;
 mod layout;
 
+use keybindings::{KeybindingEngine, UserAction};
 use layout::{ActivePane, AppLayout};
 use ratatui::layout::Rect;