diff --git a/src/game_state.rs b/src/game_state.rs
index d3efe5e..9477c50 100644
--- a/src/game_state.rs
+++ b/src/game_state.rs
@@ -1,9 +1,13 @@
 use bevy::prelude::*;
 
 use crate::components::{
-    Bullet, Enemy, EnemyBullet, GameOverUI, HighScoreText, RestartMessage, StartButton, StartMenuUI,
+    Bullet, Enemy, EnemyBullet, Explosion, GameOverUI, HighScoreText, RestartMessage, StartButton,
+    StartMenuUI,
+};
+use crate::constants::STARTING_LIVES;
+use crate::resources::{
+    CurrentStage, FormationState, HighScore, PlayerLives, RestartPressed, Score,
 };
-use crate::resources::{HighScore, RestartPressed, Score};
 
 #[derive(Clone, Eq, PartialEq, Debug, Hash, Default, States)]
 pub enum AppState {
@@ -85,7 +89,15 @@ pub fn cleanup_game_over_ui(
 
 pub fn cleanup_game_entities(
     mut commands: Commands,
-    query: Query<Entity, Or<(With<Bullet>, With<EnemyBullet>, With<Enemy>)>>,
+    query: Query<
+        Entity,
+        Or<(
+            With<Bullet>,
+            With<EnemyBullet>,
+            With<Enemy>,
+            With<Explosion>,
+        )>,
+    >,
 ) {
     for entity in &query {
         commands.entity(entity).despawn();
@@ -198,9 +210,170 @@ pub fn handle_restart_input(
 pub fn restart_game_system(
     mut next_state: ResMut<NextState<AppState>>,
     mut restart: ResMut<RestartPressed>,
+    mut score: ResMut<Score>,
+    mut lives: ResMut<PlayerLives>,
+    mut stage: ResMut<CurrentStage>,
+    mut formation: ResMut<FormationState>,
 ) {
     if restart.pressed {
         restart.pressed = false;
+        score.value = 0;
+        lives.count = STARTING_LIVES;
+        stage.number = 1;
+        stage.waiting_for_clear = false;
+        formation.next_slot_index = 0;
+        formation.total_spawned_this_stage = 0;
+        formation.formation_complete = false;
         next_state.set(AppState::Playing);
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::components::Explosion;
+    use crate::constants::STARTING_LIVES;
+    use crate::resources::{CurrentStage, FormationState, PlayerLives};
+    use bevy::ecs::world::World;
+
+    #[test]
+    fn restart_game_resets_score_to_zero() {
+        let mut world = World::default();
+        world.insert_resource(Score { value: 5000 });
+        world.insert_resource(PlayerLives { count: 1 });
+        world.insert_resource(CurrentStage {
+            number: 5,
+            waiting_for_clear: true,
+        });
+        world.insert_resource(FormationState {
+            next_slot_index: 4,
+            total_spawned_this_stage: 10,
+            formation_complete: true,
+        });
+        world.insert_resource(NextState::<AppState>::Pending(AppState::Playing));
+        world.insert_resource(RestartPressed { pressed: true });
+
+        world.register_system(restart_game_system);
+        world
+            .run_system_cached(restart_game_system)
+            .expect("system should run");
+
+        let score = world.resource::<Score>();
+        assert_eq!(score.value, 0, "Score should be reset to 0 on restart");
+    }
+
+    #[test]
+    fn restart_game_resets_player_lives_to_starting_lives() {
+        let mut world = World::default();
+        world.insert_resource(Score { value: 5000 });
+        world.insert_resource(PlayerLives { count: 1 });
+        world.insert_resource(CurrentStage {
+            number: 1,
+            waiting_for_clear: false,
+        });
+        world.insert_resource(FormationState::default());
+        world.insert_resource(NextState::<AppState>::Pending(AppState::Playing));
+        world.insert_resource(RestartPressed { pressed: true });
+
+        world.register_system(restart_game_system);
+        world
+            .run_system_cached(restart_game_system)
+            .expect("system should run");
+
+        let lives = world.resource::<PlayerLives>();
+        assert_eq!(
+            lives.count, STARTING_LIVES,
+            "PlayerLives should be reset to STARTING_LIVES on restart"
+        );
+    }
+
+    #[test]
+    fn restart_game_resets_current_stage_to_defaults() {
+        let mut world = World::default();
+        world.insert_resource(Score { value: 0 });
+        world.insert_resource(PlayerLives {
+            count: STARTING_LIVES,
+        });
+        world.insert_resource(CurrentStage {
+            number: 5,
+            waiting_for_clear: true,
+        });
+        world.insert_resource(FormationState::default());
+        world.insert_resource(NextState::<AppState>::Pending(AppState::Playing));
+        world.insert_resource(RestartPressed { pressed: true });
+
+        world.register_system(restart_game_system);
+        world
+            .run_system_cached(restart_game_system)
+            .expect("system should run");
+
+        let stage = world.resource::<CurrentStage>();
+        assert_eq!(
+            stage.number, 1,
+            "CurrentStage.number should be reset to 1 on restart"
+        );
+        assert_eq!(
+            stage.waiting_for_clear, false,
+            "CurrentStage.waiting_for_clear should be reset to false on restart"
+        );
+    }
+
+    #[test]
+    fn restart_game_resets_formation_state_to_defaults() {
+        let mut world = World::default();
+        world.insert_resource(Score { value: 0 });
+        world.insert_resource(PlayerLives {
+            count: STARTING_LIVES,
+        });
+        world.insert_resource(CurrentStage {
+            number: 1,
+            waiting_for_clear: false,
+        });
+        world.insert_resource(FormationState {
+            next_slot_index: 4,
+            total_spawned_this_stage: 10,
+            formation_complete: true,
+        });
+        world.insert_resource(NextState::<AppState>::Pending(AppState::Playing));
+        world.insert_resource(RestartPressed { pressed: true });
+
+        world.register_system(restart_game_system);
+        world
+            .run_system_cached(restart_game_system)
+            .expect("system should run");
+
+        let formation = world.resource::<FormationState>();
+        assert_eq!(
+            formation.next_slot_index, 0,
+            "FormationState.next_slot_index should be reset to 0"
+        );
+        assert_eq!(
+            formation.total_spawned_this_stage, 0,
+            "FormationState.total_spawned_this_stage should be reset to 0"
+        );
+        assert_eq!(
+            formation.formation_complete, false,
+            "FormationState.formation_complete should be reset to false"
+        );
+    }
+
+    #[test]
+    fn cleanup_game_entities_despawns_explosions() {
+        let mut world = World::default();
+        world.spawn(Explosion {
+            timer: Timer::from_seconds(0.4, TimerMode::Once),
+        });
+
+        world.register_system(cleanup_game_entities);
+        world
+            .run_system_cached(cleanup_game_entities)
+            .expect("system should run");
+
+        let mut query = world.query::<&Explosion>();
+        let explosion_count = query.iter(&world).count();
+        assert_eq!(
+            explosion_count, 0,
+            "Explosion entities should be despawned during cleanup"
+        );
+    }
+}