diff --git a/src/Domain/CombatEngine.php b/src/Domain/CombatEngine.php
index b8e65d2..edc23b2 100644
--- a/src/Domain/CombatEngine.php
+++ b/src/Domain/CombatEngine.php
@@ -76,6 +76,39 @@ final class CombatEngine
         return $next->withWinner($attacker->teamId);
     }
 
+    public function endTurn(MatchState $match): MatchState
+    {
+        $this->assertMatchActive($match);
+
+        $teamIds = [];
+
+        foreach ($match->units as $unit) {
+            $teamIds[$unit->teamId] = true;
+        }
+
+        $teamIds = array_keys($teamIds);
+        sort($teamIds);
+
+        if ($teamIds !== ['alpha', 'bravo']) {
+            throw new CombatException('Matches require alpha and bravo teams.');
+        }
+
+        $endingTeamId = $match->activeTeamId;
+        $nextTeamId = $endingTeamId === 'alpha' ? 'bravo' : 'alpha';
+        $units = [];
+
+        foreach ($match->units as $unit) {
+            $units[] = $unit->teamId === $nextTeamId ? $unit->startTurn() : $unit;
+        }
+
+        return $match->copy(
+            units: $units,
+            activeTeamId: $nextTeamId,
+            round: $match->round + ($nextTeamId === 'alpha' ? 1 : 0),
+            actionLog: [...$match->actionLog, "{$endingTeamId} ended turn"],
+        );
+    }
+
     private function unitOrFail(MatchState $match, string $unitId): UnitState
     {
         try {
diff --git a/tests/Unit/Domain/CombatEngineTest.php b/tests/Unit/Domain/CombatEngineTest.php
index 75b11ba..8c9b1aa 100644
--- a/tests/Unit/Domain/CombatEngineTest.php
+++ b/tests/Unit/Domain/CombatEngineTest.php
@@ -473,6 +473,147 @@ final class CombatEngineTest extends TestCase
         self::assertNull($next->winnerTeamId);
     }
 
+    public function testEndTurnPassesControlToBravoAndRefreshesItsLivingUnits(): void
+    {
+        $match = new MatchState(
+            new Battlefield(8, 8),
+            [
+                $this->unit(
+                    'alpha-1',
+                    'alpha',
+                    new Position(0, 0),
+                    actionsRemaining: 1,
+                    hasAttacked: true,
+                ),
+                $this->unit(
+                    'bravo-1',
+                    'bravo',
+                    new Position(7, 7),
+                    actionsRemaining: 0,
+                    hasAttacked: true,
+                ),
+            ],
+            'alpha',
+            actionLog: ['match started'],
+        );
+
+        $next = (new CombatEngine())->endTurn($match);
+
+        self::assertSame('alpha', $match->activeTeamId);
+        self::assertSame(1, $match->round);
+        self::assertSame(1, $match->unit('alpha-1')->actionsRemaining);
+        self::assertTrue($match->unit('alpha-1')->hasAttacked);
+        self::assertSame(0, $match->unit('bravo-1')->actionsRemaining);
+        self::assertTrue($match->unit('bravo-1')->hasAttacked);
+        self::assertSame(['match started'], $match->actionLog);
+        self::assertSame('bravo', $next->activeTeamId);
+        self::assertSame(1, $next->round);
+        self::assertSame(1, $next->unit('alpha-1')->actionsRemaining);
+        self::assertTrue($next->unit('alpha-1')->hasAttacked);
+        self::assertSame(2, $next->unit('bravo-1')->actionsRemaining);
+        self::assertFalse($next->unit('bravo-1')->hasAttacked);
+        self::assertSame(['match started', 'alpha ended turn'], $next->actionLog);
+    }
+
+    public function testEndTurnPassesControlToAlphaAndStartsANewRound(): void
+    {
+        $match = new MatchState(
+            new Battlefield(8, 8),
+            [
+                $this->unit(
+                    'alpha-1',
+                    'alpha',
+                    new Position(0, 0),
+                    actionsRemaining: 0,
+                    hasAttacked: true,
+                ),
+                $this->unit('bravo-1', 'bravo', new Position(7, 7), actionsRemaining: 1),
+            ],
+            'bravo',
+            round: 1,
+            actionLog: ['alpha ended turn'],
+        );
+
+        $next = (new CombatEngine())->endTurn($match);
+
+        self::assertSame('alpha', $next->activeTeamId);
+        self::assertSame(2, $next->round);
+        self::assertSame(2, $next->unit('alpha-1')->actionsRemaining);
+        self::assertFalse($next->unit('alpha-1')->hasAttacked);
+        self::assertSame(1, $next->unit('bravo-1')->actionsRemaining);
+        self::assertSame(['alpha ended turn', 'bravo ended turn'], $next->actionLog);
+        self::assertSame('bravo', $match->activeTeamId);
+        self::assertSame(1, $match->round);
+        self::assertSame(0, $match->unit('alpha-1')->actionsRemaining);
+        self::assertTrue($match->unit('alpha-1')->hasAttacked);
+        self::assertSame(['alpha ended turn'], $match->actionLog);
+    }
+
+    public function testEndTurnRejectsCompletedMatchBeforeValidatingTeams(): void
+    {
+        $match = new MatchState(
+            new Battlefield(8, 8),
+            [$this->unit('alpha-1', 'alpha', new Position(0, 0))],
+            'alpha',
+            winnerTeamId: 'alpha',
+        );
+
+        $this->expectException(CombatException::class);
+        $this->expectExceptionMessage('The match is already complete.');
+
+        (new CombatEngine())->endTurn($match);
+    }
+
+    public function testEndTurnRejectsMatchesWithoutExactlyAlphaAndBravoTeams(): void
+    {
+        $match = new MatchState(
+            new Battlefield(8, 8),
+            [
+                $this->unit('alpha-1', 'alpha', new Position(0, 0)),
+                $this->unit('charlie-1', 'charlie', new Position(7, 7)),
+            ],
+            'alpha',
+        );
+
+        $this->expectException(CombatException::class);
+        $this->expectExceptionMessage('Matches require alpha and bravo teams.');
+
+        (new CombatEngine())->endTurn($match);
+    }
+
+    public function testEndTurnDoesNotRefreshDefeatedUnitsOnIncomingTeam(): void
+    {
+        $match = new MatchState(
+            new Battlefield(8, 8),
+            [
+                $this->unit('alpha-1', 'alpha', new Position(0, 0)),
+                $this->unit(
+                    'bravo-defeated',
+                    'bravo',
+                    new Position(6, 7),
+                    health: 0,
+                    actionsRemaining: 0,
+                    hasAttacked: true,
+                ),
+                $this->unit(
+                    'bravo-living',
+                    'bravo',
+                    new Position(7, 7),
+                    actionsRemaining: 0,
+                    hasAttacked: true,
+                ),
+            ],
+            'alpha',
+        );
+
+        $next = (new CombatEngine())->endTurn($match);
+
+        self::assertSame(0, $next->unit('bravo-defeated')->actionsRemaining);
+        self::assertTrue($next->unit('bravo-defeated')->hasAttacked);
+        self::assertSame(2, $next->unit('bravo-living')->actionsRemaining);
+        self::assertFalse($next->unit('bravo-living')->hasAttacked);
+    }
+
     private function match(): MatchState
     {
         return new MatchState(