diff --git a/src/Platform/Message/AssistantMessage.php b/src/Platform/Message/AssistantMessage.php
index be60bc00..721fdade 100644
--- a/src/Platform/Message/AssistantMessage.php
+++ b/src/Platform/Message/AssistantMessage.php
@@ -5,6 +5,7 @@
 namespace PhpLlm\LlmChain\Platform\Message;
 
 use PhpLlm\LlmChain\Platform\Response\ToolCall;
+use Symfony\Component\Uid\Uuid;
 
 /**
  * @author Denis Zunke <denis.zunke@gmail.com>
@@ -25,6 +26,33 @@ public function getRole(): Role
         return Role::Assistant;
     }
 
+    public function getId(): Uuid
+    {
+        // Generate deterministic UUID based on content, role, and tool calls
+        $toolCallsData = '';
+        if ($this->toolCalls !== null) {
+            $toolCallsData = serialize(array_map(
+                static fn (ToolCall $toolCall) => [
+                    'id' => $toolCall->id,
+                    'name' => $toolCall->name,
+                    'arguments' => $toolCall->arguments,
+                ],
+                $this->toolCalls
+            ));
+        }
+
+        $data = sprintf('assistant:%s:%s', $this->content ?? '', $toolCallsData);
+
+        return Uuid::v5(self::getNamespace(), $data);
+    }
+
+    private static function getNamespace(): Uuid
+    {
+        // Use a fixed namespace UUID for the LLM Chain message system
+        // This ensures deterministic IDs across application runs
+        return Uuid::fromString('6ba7b810-9dad-11d1-80b4-00c04fd430c8');
+    }
+
     public function hasToolCalls(): bool
     {
         return null !== $this->toolCalls && 0 !== \count($this->toolCalls);
diff --git a/src/Platform/Message/MessageBag.php b/src/Platform/Message/MessageBag.php
index 45d4db35..1966357c 100644
--- a/src/Platform/Message/MessageBag.php
+++ b/src/Platform/Message/MessageBag.php
@@ -4,6 +4,8 @@
 
 namespace PhpLlm\LlmChain\Platform\Message;
 
+use Symfony\Component\Uid\Uuid;
+
 /**
  * @final
  *
@@ -102,6 +104,76 @@ public function containsImage(): bool
         return false;
     }
 
+    /**
+     * Get all messages that come after a message with the specified ID.
+     * If the ID is not found, returns all messages.
+     *
+     * @return list<MessageInterface>
+     */
+    public function messagesAfterId(Uuid $id): array
+    {
+        $found = false;
+        $messagesAfter = [];
+
+        foreach ($this->messages as $message) {
+            if ($found) {
+                $messagesAfter[] = $message;
+            } elseif ($message->getId()->equals($id)) {
+                $found = true;
+            }
+        }
+
+        // If ID not found, return all messages
+        return $found ? $messagesAfter : $this->messages;
+    }
+
+    /**
+     * Get messages newer than (excluding) the specified ID.
+     *
+     * @return self
+     */
+    public function messagesNewerThan(Uuid $id): self
+    {
+        $messagesAfter = $this->messagesAfterId($id);
+
+        return new self(...$messagesAfter);
+    }
+
+    /**
+     * Find a message by its ID.
+     */
+    public function findById(Uuid $id): ?MessageInterface
+    {
+        foreach ($this->messages as $message) {
+            if ($message->getId()->equals($id)) {
+                return $message;
+            }
+        }
+
+        return null;
+    }
+
+    /**
+     * Check if a message with the specified ID exists in the bag.
+     */
+    public function hasMessageWithId(Uuid $id): bool
+    {
+        return $this->findById($id) !== null;
+    }
+
+    /**
+     * Get all IDs in the message bag in order.
+     *
+     * @return list<Uuid>
+     */
+    public function getIds(): array
+    {
+        return array_map(
+            static fn (MessageInterface $message) => $message->getId(),
+            $this->messages
+        );
+    }
+
     public function count(): int
     {
         return \count($this->messages);
diff --git a/src/Platform/Message/MessageBagInterface.php b/src/Platform/Message/MessageBagInterface.php
index d806bd31..87bba416 100644
--- a/src/Platform/Message/MessageBagInterface.php
+++ b/src/Platform/Message/MessageBagInterface.php
@@ -4,6 +4,8 @@
 
 namespace PhpLlm\LlmChain\Platform\Message;
 
+use Symfony\Component\Uid\Uuid;
+
 /**
  * @author Oskar Stark <oskarstark@googlemail.com>
  */
@@ -29,4 +31,34 @@ public function prepend(MessageInterface $message): self;
     public function containsAudio(): bool;
 
     public function containsImage(): bool;
+
+    /**
+     * Get all messages that come after a message with the specified ID.
+     * If the ID is not found, returns all messages.
+     *
+     * @return list<MessageInterface>
+     */
+    public function messagesAfterId(Uuid $id): array;
+
+    /**
+     * Get messages newer than (excluding) the specified ID.
+     */
+    public function messagesNewerThan(Uuid $id): self;
+
+    /**
+     * Find a message by its ID.
+     */
+    public function findById(Uuid $id): ?MessageInterface;
+
+    /**
+     * Check if a message with the specified ID exists in the bag.
+     */
+    public function hasMessageWithId(Uuid $id): bool;
+
+    /**
+     * Get all IDs in the message bag in order.
+     *
+     * @return list<Uuid>
+     */
+    public function getIds(): array;
 }
diff --git a/src/Platform/Message/MessageInterface.php b/src/Platform/Message/MessageInterface.php
index eabf13fc..0b9f0865 100644
--- a/src/Platform/Message/MessageInterface.php
+++ b/src/Platform/Message/MessageInterface.php
@@ -4,10 +4,14 @@
 
 namespace PhpLlm\LlmChain\Platform\Message;
 
+use Symfony\Component\Uid\Uuid;
+
 /**
  * @author Denis Zunke <denis.zunke@gmail.com>
  */
 interface MessageInterface
 {
     public function getRole(): Role;
+
+    public function getId(): Uuid;
 }
diff --git a/src/Platform/Message/SystemMessage.php b/src/Platform/Message/SystemMessage.php
index 59c3e3b2..c759b02e 100644
--- a/src/Platform/Message/SystemMessage.php
+++ b/src/Platform/Message/SystemMessage.php
@@ -4,6 +4,8 @@
 
 namespace PhpLlm\LlmChain\Platform\Message;
 
+use Symfony\Component\Uid\Uuid;
+
 /**
  * @author Denis Zunke <denis.zunke@gmail.com>
  */
@@ -17,4 +19,19 @@ public function getRole(): Role
     {
         return Role::System;
     }
+
+    public function getId(): Uuid
+    {
+        // Generate deterministic UUID based on content and role
+        $data = sprintf('system:%s', $this->content);
+
+        return Uuid::v5(self::getNamespace(), $data);
+    }
+
+    private static function getNamespace(): Uuid
+    {
+        // Use a fixed namespace UUID for the LLM Chain message system
+        // This ensures deterministic IDs across application runs
+        return Uuid::fromString('6ba7b810-9dad-11d1-80b4-00c04fd430c8');
+    }
 }
diff --git a/src/Platform/Message/ToolCallMessage.php b/src/Platform/Message/ToolCallMessage.php
index 09876007..3e6e31d0 100644
--- a/src/Platform/Message/ToolCallMessage.php
+++ b/src/Platform/Message/ToolCallMessage.php
@@ -5,6 +5,7 @@
 namespace PhpLlm\LlmChain\Platform\Message;
 
 use PhpLlm\LlmChain\Platform\Response\ToolCall;
+use Symfony\Component\Uid\Uuid;
 
 /**
  * @author Denis Zunke <denis.zunke@gmail.com>
@@ -21,4 +22,20 @@ public function getRole(): Role
     {
         return Role::ToolCall;
     }
+
+    public function getId(): Uuid
+    {
+        // Generate deterministic UUID based on tool call and content
+        $toolCallData = sprintf('%s:%s:%s', $this->toolCall->id, $this->toolCall->name, serialize($this->toolCall->arguments));
+        $data = sprintf('toolcall:%s:%s', $toolCallData, $this->content);
+
+        return Uuid::v5(self::getNamespace(), $data);
+    }
+
+    private static function getNamespace(): Uuid
+    {
+        // Use a fixed namespace UUID for the LLM Chain message system
+        // This ensures deterministic IDs across application runs
+        return Uuid::fromString('6ba7b810-9dad-11d1-80b4-00c04fd430c8');
+    }
 }
diff --git a/src/Platform/Message/UserMessage.php b/src/Platform/Message/UserMessage.php
index f379f503..28a3811b 100644
--- a/src/Platform/Message/UserMessage.php
+++ b/src/Platform/Message/UserMessage.php
@@ -8,6 +8,7 @@
 use PhpLlm\LlmChain\Platform\Message\Content\ContentInterface;
 use PhpLlm\LlmChain\Platform\Message\Content\Image;
 use PhpLlm\LlmChain\Platform\Message\Content\ImageUrl;
+use Symfony\Component\Uid\Uuid;
 
 /**
  * @author Denis Zunke <denis.zunke@gmail.com>
@@ -30,6 +31,22 @@ public function getRole(): Role
         return Role::User;
     }
 
+    public function getId(): Uuid
+    {
+        // Generate deterministic UUID based on content and role
+        $contentData = serialize($this->content);
+        $data = sprintf('user:%s', $contentData);
+
+        return Uuid::v5(self::getNamespace(), $data);
+    }
+
+    private static function getNamespace(): Uuid
+    {
+        // Use a fixed namespace UUID for the LLM Chain message system
+        // This ensures deterministic IDs across application runs
+        return Uuid::fromString('6ba7b810-9dad-11d1-80b4-00c04fd430c8');
+    }
+
     public function hasAudioContent(): bool
     {
         foreach ($this->content as $content) {
diff --git a/tests/Platform/Message/MessageIdTest.php b/tests/Platform/Message/MessageIdTest.php
new file mode 100644
index 00000000..4344797e
--- /dev/null
+++ b/tests/Platform/Message/MessageIdTest.php
@@ -0,0 +1,211 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpLlm\LlmChain\Tests\Platform\Message;
+
+use PhpLlm\LlmChain\Platform\Message\AssistantMessage;
+use PhpLlm\LlmChain\Platform\Message\Content\Text;
+use PhpLlm\LlmChain\Platform\Message\Message;
+use PhpLlm\LlmChain\Platform\Message\MessageBag;
+use PhpLlm\LlmChain\Platform\Message\Role;
+use PhpLlm\LlmChain\Platform\Message\SystemMessage;
+use PhpLlm\LlmChain\Platform\Message\ToolCallMessage;
+use PhpLlm\LlmChain\Platform\Message\UserMessage;
+use PhpLlm\LlmChain\Platform\Response\ToolCall;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Small;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\Attributes\UsesClass;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Uid\Uuid;
+
+#[CoversClass(SystemMessage::class)]
+#[CoversClass(AssistantMessage::class)]
+#[CoversClass(UserMessage::class)]
+#[CoversClass(ToolCallMessage::class)]
+#[CoversClass(MessageBag::class)]
+#[UsesClass(Message::class)]
+#[UsesClass(Role::class)]
+#[UsesClass(ToolCall::class)]
+#[UsesClass(Text::class)]
+#[Small]
+final class MessageIdTest extends TestCase
+{
+    #[Test]
+    public function systemMessageHasDeterministicId(): void
+    {
+        $message1 = Message::forSystem('System prompt');
+        $message2 = Message::forSystem('System prompt');
+        $message3 = Message::forSystem('Different prompt');
+
+        self::assertNotEmpty($message1->getId());
+        self::assertTrue($message1->getId()->equals($message2->getId()));
+        self::assertFalse($message1->getId()->equals($message3->getId()));
+    }
+
+    #[Test]
+    public function assistantMessageHasDeterministicId(): void
+    {
+        $message1 = Message::ofAssistant('Hello there');
+        $message2 = Message::ofAssistant('Hello there');
+        $message3 = Message::ofAssistant('Different content');
+
+        self::assertNotEmpty($message1->getId());
+        self::assertTrue($message1->getId()->equals($message2->getId()));
+        self::assertFalse($message1->getId()->equals($message3->getId()));
+    }
+
+    #[Test]
+    public function assistantMessageWithToolCallsHasDeterministicId(): void
+    {
+        $toolCall1 = new ToolCall('call_123', 'test_tool', ['param' => 'value']);
+        $toolCall2 = new ToolCall('call_456', 'other_tool');
+
+        $message1 = Message::ofAssistant('Content', [$toolCall1]);
+        $message2 = Message::ofAssistant('Content', [$toolCall1]);
+        $message3 = Message::ofAssistant('Content', [$toolCall2]);
+        $message4 = Message::ofAssistant('Different content', [$toolCall1]);
+
+        self::assertNotEmpty($message1->getId());
+        self::assertTrue($message1->getId()->equals($message2->getId()));
+        self::assertFalse($message1->getId()->equals($message3->getId()));
+        self::assertFalse($message1->getId()->equals($message4->getId()));
+    }
+
+    #[Test]
+    public function userMessageHasDeterministicId(): void
+    {
+        $message1 = Message::ofUser('Hello');
+        $message2 = Message::ofUser('Hello');
+        $message3 = Message::ofUser('Different message');
+
+        self::assertNotEmpty($message1->getId());
+        self::assertTrue($message1->getId()->equals($message2->getId()));
+        self::assertFalse($message1->getId()->equals($message3->getId()));
+    }
+
+    #[Test]
+    public function toolCallMessageHasDeterministicId(): void
+    {
+        $toolCall1 = new ToolCall('call_123', 'test_tool', ['param' => 'value']);
+        $toolCall2 = new ToolCall('call_456', 'other_tool');
+
+        $message1 = Message::ofToolCall($toolCall1, 'Result 1');
+        $message2 = Message::ofToolCall($toolCall1, 'Result 1');
+        $message3 = Message::ofToolCall($toolCall2, 'Result 1');
+        $message4 = Message::ofToolCall($toolCall1, 'Result 2');
+
+        self::assertNotEmpty($message1->getId());
+        self::assertTrue($message1->getId()->equals($message2->getId()));
+        self::assertFalse($message1->getId()->equals($message3->getId()));
+        self::assertFalse($message1->getId()->equals($message4->getId()));
+    }
+
+    #[Test]
+    public function differentMessageTypesHaveDifferentIds(): void
+    {
+        $content = 'Same content';
+
+        $systemMessage = Message::forSystem($content);
+        $assistantMessage = Message::ofAssistant($content);
+        $userMessage = Message::ofUser($content);
+
+        self::assertFalse($systemMessage->getId()->equals($assistantMessage->getId()));
+        self::assertFalse($systemMessage->getId()->equals($userMessage->getId()));
+        self::assertFalse($assistantMessage->getId()->equals($userMessage->getId()));
+    }
+
+    #[Test]
+    public function messageBagCanFindMessageById(): void
+    {
+        $message1 = Message::forSystem('System');
+        $message2 = Message::ofUser('User message');
+        $message3 = Message::ofAssistant('Assistant response');
+
+        $bag = new MessageBag($message1, $message2, $message3);
+
+        self::assertSame($message1, $bag->findById($message1->getId()));
+        self::assertSame($message2, $bag->findById($message2->getId()));
+        self::assertSame($message3, $bag->findById($message3->getId()));
+        self::assertNull($bag->findById(Uuid::v4())); // Random UUID
+    }
+
+    #[Test]
+    public function messageBagCanCheckIfIdExists(): void
+    {
+        $message1 = Message::forSystem('System');
+        $message2 = Message::ofUser('User message');
+
+        $bag = new MessageBag($message1, $message2);
+
+        self::assertTrue($bag->hasMessageWithId($message1->getId()));
+        self::assertTrue($bag->hasMessageWithId($message2->getId()));
+        self::assertFalse($bag->hasMessageWithId(Uuid::v4())); // Random UUID
+    }
+
+    #[Test]
+    public function messageBagCanGetAllIds(): void
+    {
+        $message1 = Message::forSystem('System');
+        $message2 = Message::ofUser('User message');
+        $message3 = Message::ofAssistant('Assistant response');
+
+        $bag = new MessageBag($message1, $message2, $message3);
+        $ids = $bag->getIds();
+
+        self::assertCount(3, $ids);
+        self::assertTrue($message1->getId()->equals($ids[0]));
+        self::assertTrue($message2->getId()->equals($ids[1]));
+        self::assertTrue($message3->getId()->equals($ids[2]));
+    }
+
+    #[Test]
+    public function messageBagCanGetMessagesAfterId(): void
+    {
+        $message1 = Message::forSystem('System');
+        $message2 = Message::ofUser('User message');
+        $message3 = Message::ofAssistant('Assistant response');
+        $message4 = Message::ofUser('Another user message');
+
+        $bag = new MessageBag($message1, $message2, $message3, $message4);
+
+        $messagesAfterMessage2 = $bag->messagesAfterId($message2->getId());
+        self::assertCount(2, $messagesAfterMessage2);
+        self::assertSame($message3, $messagesAfterMessage2[0]);
+        self::assertSame($message4, $messagesAfterMessage2[1]);
+
+        // If ID not found, should return all messages
+        $allMessages = $bag->messagesAfterId(Uuid::v4()); // Random UUID
+        self::assertCount(4, $allMessages);
+    }
+
+    #[Test]
+    public function messageBagCanGetMessagesNewerThan(): void
+    {
+        $message1 = Message::forSystem('System');
+        $message2 = Message::ofUser('User message');
+        $message3 = Message::ofAssistant('Assistant response');
+        $message4 = Message::ofUser('Another user message');
+
+        $bag = new MessageBag($message1, $message2, $message3, $message4);
+
+        $newerBag = $bag->messagesNewerThan($message1->getId());
+        $newerMessages = $newerBag->getMessages();
+
+        self::assertCount(3, $newerMessages);
+        self::assertSame($message2, $newerMessages[0]);
+        self::assertSame($message3, $newerMessages[1]);
+        self::assertSame($message4, $newerMessages[2]);
+    }
+
+    #[Test]
+    public function idIsValidUuid(): void
+    {
+        $message = Message::forSystem('Test message');
+        $id = $message->getId();
+
+        // Should be a valid UUID
+        self::assertInstanceOf(Uuid::class, $id);
+    }
+}