diff --git a/src/Helpers/InMemoryEventStore.php b/src/Helpers/InMemoryEventStore.php
index cb4c442..ddae208 100644
--- a/src/Helpers/InMemoryEventStore.php
+++ b/src/Helpers/InMemoryEventStore.php
@@ -4,6 +4,7 @@
 
 namespace Wwwision\DCBEventStore\Helpers;
 
+use DateTimeImmutable;
 use Wwwision\DCBEventStore\EventStore;
 use Wwwision\DCBEventStore\Exceptions\ConditionalAppendFailed;
 use Wwwision\DCBEventStore\Types\AppendCondition;
@@ -84,6 +85,7 @@ public function append(Events $events, AppendCondition $condition): void
             $sequenceNumber++;
             $this->eventEnvelopes[] = new EventEnvelope(
                 SequenceNumber::fromInteger($sequenceNumber),
+                new DateTimeImmutable(),
                 $event,
             );
         }
diff --git a/src/Types/Event.php b/src/Types/Event.php
index a35c45f..411eb4b 100644
--- a/src/Types/Event.php
+++ b/src/Types/Event.php
@@ -14,7 +14,7 @@ public function __construct(
         public readonly EventType $type,
         public readonly EventData $data, // opaque, no size limit?
         public readonly Tags $tags,
-        // add metadata ?
+        public readonly EventMetadata $metadata,
     ) {
     }
 }
diff --git a/src/Types/EventEnvelope.php b/src/Types/EventEnvelope.php
index 685de06..6e8da1d 100644
--- a/src/Types/EventEnvelope.php
+++ b/src/Types/EventEnvelope.php
@@ -8,14 +8,12 @@
 
 /**
  * An {@see Event} with its global {@see SequenceNumber} in the Events Store
- *
- *
  */
 final class EventEnvelope
 {
     public function __construct(
         public readonly SequenceNumber $sequenceNumber,
-        //public DateTimeImmutable $recordedAt, // do we need it
+        public DateTimeImmutable $recordedAt,
         public readonly Event $event,
     ) {
     }
diff --git a/src/Types/EventMetadata.php b/src/Types/EventMetadata.php
new file mode 100644
index 0000000..573f85d
--- /dev/null
+++ b/src/Types/EventMetadata.php
@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Wwwision\DCBEventStore\Types;
+
+use InvalidArgumentException;
+use JsonException;
+use JsonSerializable;
+use Webmozart\Assert\Assert;
+
+/**
+ * Array-based metadata of an event
+ */
+final class EventMetadata implements JsonSerializable
+{
+    /**
+     * @param array<string, mixed> $value
+     */
+    private function __construct(
+        public readonly array $value,
+    ) {
+        Assert::isMap($value, 'EventMetadata must consist of an associative array with string keys');
+    }
+
+    public static function none(): self
+    {
+        return new self([]);
+    }
+
+    /**
+     * @param array<string, mixed> $value
+     */
+    public static function fromArray(array $value): self
+    {
+        return new self($value);
+    }
+
+    public static function fromJson(string $json): self
+    {
+        try {
+            $metadata = json_decode($json, true, 512, JSON_THROW_ON_ERROR);
+        } catch (JsonException $e) {
+            throw new InvalidArgumentException(sprintf('Failed to decode JSON to event metadata: %s', $e->getMessage()), 1692197194, $e);
+        }
+        Assert::isArray($metadata, 'Failed to decode JSON to event metadata');
+        return self::fromArray($metadata);
+    }
+
+    public function with(string $key, mixed $value): self
+    {
+        return new self([...$this->value, $key => $value]);
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function jsonSerialize(): array
+    {
+        return $this->value;
+    }
+}
diff --git a/src/Types/Events.php b/src/Types/Events.php
index 4ec0017..a6becb6 100644
--- a/src/Types/Events.php
+++ b/src/Types/Events.php
@@ -30,9 +30,9 @@ private function __construct(Event ...$events)
         $this->events = $events;
     }
 
-    public static function single(EventId $id, EventType $type, EventData $data, Tags $tags): self
+    public static function single(EventId $id, EventType $type, EventData $data, Tags $tags, EventMetadata $metadata): self
     {
-        return new self(new Event($id, $type, $data, $tags));
+        return new self(new Event($id, $type, $data, $tags, $metadata));
     }
 
     /**
diff --git a/tests/Integration/EventStoreConcurrencyTestBase.php b/tests/Integration/EventStoreConcurrencyTestBase.php
index 2923bc9..18a3502 100644
--- a/tests/Integration/EventStoreConcurrencyTestBase.php
+++ b/tests/Integration/EventStoreConcurrencyTestBase.php
@@ -10,6 +10,7 @@
 use Wwwision\DCBEventStore\EventStore;
 use Wwwision\DCBEventStore\Exceptions\ConditionalAppendFailed;
 use Wwwision\DCBEventStore\Types\AppendCondition;
+use Wwwision\DCBEventStore\Types\EventMetadata;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria\EventTypesAndTagsCriterion;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria\EventTypesCriterion;
@@ -89,7 +90,7 @@ public function test_consistency(int $process): void
             for ($i = 0; $i < $numberOfEvents; $i++) {
                 $descriptor = $process . '(' . getmypid() . ') ' . $eventBatch . '.' . ($i + 1) . '/' . $numberOfEvents;
                 $eventData = $i > 0 ? ['descriptor' => $descriptor] : ['query' => StreamQuerySerializer::serialize($query), 'expectedHighestSequenceNumber' => $expectedHighestSequenceNumber->isNone() ? null : $expectedHighestSequenceNumber->extractSequenceNumber()->value, 'descriptor' => $descriptor];
-                $events[] = new Event(EventId::create(), self::either(...$eventTypes), EventData::fromString(json_encode($eventData, JSON_THROW_ON_ERROR)), Tags::create(...self::some($numberOfTags, ...$tags)));
+                $events[] = new Event(EventId::create(), self::either(...$eventTypes), EventData::fromString(json_encode($eventData, JSON_THROW_ON_ERROR)), Tags::create(...self::some($numberOfTags, ...$tags)), EventMetadata::none());
             }
             try {
                 static::createEventStore()->append(Events::fromArray($events), new AppendCondition($query, $expectedHighestSequenceNumber));
diff --git a/tests/Integration/EventStoreTestBase.php b/tests/Integration/EventStoreTestBase.php
index 10d90eb..81155d3 100644
--- a/tests/Integration/EventStoreTestBase.php
+++ b/tests/Integration/EventStoreTestBase.php
@@ -8,6 +8,7 @@
 use Wwwision\DCBEventStore\EventStream;
 use Wwwision\DCBEventStore\Exceptions\ConditionalAppendFailed;
 use Wwwision\DCBEventStore\Types\AppendCondition;
+use Wwwision\DCBEventStore\Types\EventMetadata;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria\EventTypesAndTagsCriterion;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria\EventTypesCriterion;
@@ -398,6 +399,7 @@ private static function arrayToEvent(array $event): Event
             EventType::fromString($event['type'] ?? 'SomeEventType'),
             EventData::fromString($event['data'] ?? ''),
             Tags::fromArray($event['tags'] ?? ['foo:bar']),
+            EventMetadata::fromArray($event['metadata'] ?? ['foo' => 'bar']),
         );
     }
 }
\ No newline at end of file
diff --git a/tests/Unit/Types/EventMetadataTest.php b/tests/Unit/Types/EventMetadataTest.php
new file mode 100644
index 0000000..cd0d609
--- /dev/null
+++ b/tests/Unit/Types/EventMetadataTest.php
@@ -0,0 +1,60 @@
+<?php
+declare(strict_types=1);
+
+namespace Unit\Types;
+
+use InvalidArgumentException;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Wwwision\DCBEventStore\Types\EventMetadata;
+
+#[CoversClass(EventMetadata::class)]
+final class EventMetadataTest extends TestCase
+{
+
+    public function test_none_creates_empty_instance(): void
+    {
+        self::assertSame([], EventMetadata::none()->value);
+    }
+
+    public function test_fromArray_fails_if_array_is_not_associative(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        EventMetadata::fromArray(['foo', 'bar']);
+    }
+
+    public function test_fromJson_fails_if_value_is_no_valid_json(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        EventMetadata::fromJson('no json');
+    }
+
+    public function test_fromJson_fails_if_value_is_no_json_object(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        EventMetadata::fromJson('"no array"');
+    }
+
+    public function test_fromJson_fails_if_value_is_no_associative_json_object(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        EventMetadata::fromJson('["foo", "bar"]');
+    }
+
+    public function test_with_sets_metadata_value(): void
+    {
+        self::assertSame(['foo' => 'bar'], EventMetadata::none()->with('foo', 'bar')->value);
+    }
+
+    public function test_with_overrides_previously_set_value(): void
+    {
+        self::assertSame(['foo' => 'replaced'], EventMetadata::none()->with('foo', 'bar')->with('foo', 'replaced')->value);
+    }
+
+    public function test_jsonSerializable(): void
+    {
+        $actualResult = json_encode(EventMetadata::none()->with('foo', 'bar')->with('bar', 'baz'));
+        self::assertJsonStringEqualsJsonString('{"foo": "bar", "bar": "baz"}', $actualResult);
+    }
+
+}
\ No newline at end of file
diff --git a/tests/Unit/Types/EventTypesTest.php b/tests/Unit/Types/EventTypesTest.php
index a1744c1..b0cf483 100644
--- a/tests/Unit/Types/EventTypesTest.php
+++ b/tests/Unit/Types/EventTypesTest.php
@@ -10,6 +10,7 @@
 use Wwwision\DCBEventStore\Types\EventTypes;
 
 #[CoversClass(EventTypes::class)]
+#[CoversClass(EventType::class)]
 final class EventTypesTest extends TestCase
 {
 
diff --git a/tests/Unit/Types/StreamQuery/StreamQueryTest.php b/tests/Unit/Types/StreamQuery/StreamQueryTest.php
index c9df8f3..5d59ed4 100644
--- a/tests/Unit/Types/StreamQuery/StreamQueryTest.php
+++ b/tests/Unit/Types/StreamQuery/StreamQueryTest.php
@@ -8,6 +8,7 @@
 use Wwwision\DCBEventStore\Types\Event;
 use Wwwision\DCBEventStore\Types\EventData;
 use Wwwision\DCBEventStore\Types\EventId;
+use Wwwision\DCBEventStore\Types\EventMetadata;
 use Wwwision\DCBEventStore\Types\EventType;
 use Wwwision\DCBEventStore\Types\EventTypes;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria;
@@ -15,11 +16,17 @@
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria\EventTypesCriterion;
 use Wwwision\DCBEventStore\Types\StreamQuery\Criteria\TagsCriterion;
 use Wwwision\DCBEventStore\Types\StreamQuery\StreamQuery;
+use Wwwision\DCBEventStore\Types\Tag;
 use Wwwision\DCBEventStore\Types\Tags;
 
 #[CoversClass(StreamQuery::class)]
 #[CoversClass(Tags::class)]
+#[CoversClass(Tag::class)]
 #[CoversClass(EventTypes::class)]
+#[CoversClass(Criteria::class)]
+#[CoversClass(TagsCriterion::class)]
+#[CoversClass(EventTypesCriterion::class)]
+#[CoversClass(EventTypesAndTagsCriterion::class)]
 final class StreamQueryTest extends TestCase
 {
 
@@ -27,7 +34,7 @@ public static function dataprovider_no_match(): iterable
     {
         $eventType = EventType::fromString('SomeEventType');
         $tags = Tags::fromArray(['foo:bar', 'bar:baz']);
-        $event = new Event(EventId::create(), $eventType, EventData::fromString(''), $tags);
+        $event = new Event(EventId::create(), $eventType, EventData::fromString(''), $tags, EventMetadata::none());
 
         yield 'different tag' => ['query' => StreamQuery::create(Criteria::create(new TagsCriterion(Tags::single('foo', 'not_bar')))), 'event' => $event];
         yield 'different event type' => ['query' => StreamQuery::create(Criteria::create(new EventTypesCriterion(EventTypes::single('SomeOtherEventType')))), 'event' => $event];
@@ -35,7 +42,7 @@ public static function dataprovider_no_match(): iterable
         yield 'matching all tags plus additional tags' => ['query' => StreamQuery::create(Criteria::create(new TagsCriterion(Tags::fromArray(['foo:bar', 'bar:baz', 'foos:bars'])))), 'event' => $event];
 
         yield 'partially matching tags' => ['query' => StreamQuery::create(Criteria::create(new TagsCriterion(Tags::fromArray(['foo:bar', 'bar:not_baz'])))), 'event' => $event];
-        yield 'matching tag, different event type' => ['query' => StreamQuery::create(Criteria::create(new EventTypesAndTagsCriterion(EventTypes::single('Event4'), Tags::fromArray(['key2:value1', 'key1:value3'])))), 'event' => new Event(EventId::create(), EventType::fromString('Event3'), EventData::fromString(''), Tags::single('key2', 'value1'))];
+        yield 'matching tag, different event type' => ['query' => StreamQuery::create(Criteria::create(new EventTypesAndTagsCriterion(EventTypes::single('Event4'), Tags::fromArray(['key2:value1', 'key1:value3'])))), 'event' => new Event(EventId::create(), EventType::fromString('Event3'), EventData::fromString(''), Tags::single('key2', 'value1'), EventMetadata::none())];
     }
 
     /**
@@ -50,7 +57,7 @@ public static function dataprovider_matches(): iterable
     {
         $eventType = EventType::fromString('SomeEventType');
         $tags = Tags::fromArray(['foo:bar', 'bar:baz']);
-        $event = new Event(EventId::create(), $eventType, EventData::fromString(''), $tags);
+        $event = new Event(EventId::create(), $eventType, EventData::fromString(''), $tags, EventMetadata::none());
 
         yield 'matching tag type and value' => ['query' => StreamQuery::create(Criteria::create(new TagsCriterion(Tags::single('foo', 'bar')))), 'event' => $event];
         yield 'matching event type' => ['query' => StreamQuery::create(Criteria::create(new EventTypesCriterion(EventTypes::single('SomeEventType')))), 'event' => $event];
diff --git a/tests/Unit/Types/TagsTest.php b/tests/Unit/Types/TagsTest.php
index 4ccc9c5..656e45f 100644
--- a/tests/Unit/Types/TagsTest.php
+++ b/tests/Unit/Types/TagsTest.php
@@ -13,6 +13,7 @@
 use const JSON_THROW_ON_ERROR;
 
 #[CoversClass(Tags::class)]
+#[CoversClass(Tag::class)]
 final class TagsTest extends TestCase
 {