diff --git a/README.md b/README.md
index b826123..2a91e1c 100644
--- a/README.md
+++ b/README.md
@@ -208,9 +208,29 @@ final class AnotherDto
 }
 ```
 
+#### Union Object
+
+If you have a union type from multiple classes, then you can use the `UnionObjectNormalizer` normalizer
+
+```php
+use Patchlevel\Hydrator\Normalizer\UnionObjectNormalizer;
+
+final class DTO
+{
+    #[UnionObjectNormalizer([
+        Foo::class => 'foo',
+        Bar::class => 'bar'
+    ])]
+    public Foo|Bar|null $object;
+}
+```
+
 > [!WARNING]
 > Circular references are not supported and will result in an exception.
 
+> [!NOTE]
+> Auto detection of the type is not possible. You have to specify the type yourself.
+
 ### Custom Normalizer
 
 Since we only offer normalizers for PHP native things,
diff --git a/baseline.xml b/baseline.xml
index d3e4ee0..411e039 100644
--- a/baseline.xml
+++ b/baseline.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<files psalm-version="5.22.2@d768d914152dbbf3486c36398802f74e80cfde48">
+<files psalm-version="5.23.1@8471a896ccea3526b26d082f4461eeea467f10a4">
   <file src="src/Normalizer/ObjectNormalizer.php">
     <MixedArgument>
       <code><![CDATA[$value]]></code>
@@ -8,4 +8,9 @@
       <code><![CDATA[$value]]></code>
     </MixedArgumentTypeCoercion>
   </file>
+  <file src="src/Normalizer/UnionObjectNormalizer.php">
+    <MixedArgumentTypeCoercion>
+      <code><![CDATA[$value]]></code>
+    </MixedArgumentTypeCoercion>
+  </file>
 </files>
diff --git a/src/Normalizer/UnionObjectNormalizer.php b/src/Normalizer/UnionObjectNormalizer.php
new file mode 100644
index 0000000..28aabf5
--- /dev/null
+++ b/src/Normalizer/UnionObjectNormalizer.php
@@ -0,0 +1,121 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\Hydrator\Normalizer;
+
+use Attribute;
+use Patchlevel\Hydrator\Hydrator;
+
+use function array_flip;
+use function array_key_exists;
+use function array_keys;
+use function implode;
+use function is_array;
+use function is_object;
+use function is_string;
+use function sprintf;
+
+#[Attribute(Attribute::TARGET_PROPERTY)]
+final class UnionObjectNormalizer implements Normalizer, HydratorAwareNormalizer
+{
+    private Hydrator|null $hydrator = null;
+
+    /** @var array<string, class-string> */
+    private array $typeToClassMap;
+
+    /** @param array<class-string, string> $classToTypeMap */
+    public function __construct(
+        private readonly array|null $classToTypeMap = null,
+        private readonly string $typeFieldName = '_type',
+    ) {
+        $this->typeToClassMap = array_flip($classToTypeMap);
+    }
+
+    public function setHydrator(Hydrator $hydrator): void
+    {
+        $this->hydrator = $hydrator;
+    }
+
+    public function normalize(mixed $value): mixed
+    {
+        if (!$this->hydrator) {
+            throw new MissingHydrator();
+        }
+
+        if ($value === null) {
+            return null;
+        }
+
+        if (!is_object($value)) {
+            throw InvalidArgument::withWrongType(
+                sprintf('%s|null', implode('|', array_keys($this->classToTypeMap))),
+                $value,
+            );
+        }
+
+        if (!array_key_exists($value::class, $this->classToTypeMap)) {
+            throw InvalidArgument::withWrongType(
+                sprintf('%s|null', implode('|', array_keys($this->classToTypeMap))),
+                $value,
+            );
+        }
+
+        $data = $this->hydrator->extract($value);
+        $data[$this->typeFieldName] = $this->classToTypeMap[$value::class];
+
+        return $data;
+    }
+
+    public function denormalize(mixed $value): mixed
+    {
+        if (!$this->hydrator) {
+            throw new MissingHydrator();
+        }
+
+        if ($value === null) {
+            return null;
+        }
+
+        if (!is_array($value)) {
+            throw InvalidArgument::withWrongType('array<string, mixed>|null', $value);
+        }
+
+        if (!array_key_exists($this->typeFieldName, $value)) {
+            throw new InvalidArgument(sprintf('missing type field "%s"', $this->typeFieldName));
+        }
+
+        $type = $value[$this->typeFieldName];
+
+        if (!is_string($type)) {
+            throw InvalidArgument::withWrongType('string', $type);
+        }
+
+        if (!array_key_exists($type, $this->typeToClassMap)) {
+            throw new InvalidArgument(sprintf('unknown type "%s"', $type));
+        }
+
+        $className = $this->typeToClassMap[$type];
+        unset($value[$this->typeFieldName]);
+
+        return $this->hydrator->hydrate($className, $value);
+    }
+
+    /**
+     * @return array{
+     *     typeToClassMap: array<string, class-string>,
+     *     classToTypeMap: array<class-string, string>,
+     *     typeFieldName: string,
+     *     hydrator: null
+     * }
+     */
+    public function __serialize(): array
+    {
+        return [
+            'typeToClassMap' => $this->typeToClassMap,
+            'classToTypeMap' => $this->classToTypeMap,
+            'typeFieldName' => $this->typeFieldName,
+            'hydrator' => null,
+        ];
+    }
+}
diff --git a/tests/Unit/Normalizer/UnionObjectNormalizerTest.php b/tests/Unit/Normalizer/UnionObjectNormalizerTest.php
new file mode 100644
index 0000000..eb57a85
--- /dev/null
+++ b/tests/Unit/Normalizer/UnionObjectNormalizerTest.php
@@ -0,0 +1,143 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Patchlevel\Hydrator\Tests\Unit\Normalizer;
+
+use Attribute;
+use Patchlevel\Hydrator\Hydrator;
+use Patchlevel\Hydrator\Normalizer\InvalidArgument;
+use Patchlevel\Hydrator\Normalizer\MissingHydrator;
+use Patchlevel\Hydrator\Normalizer\UnionObjectNormalizer;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\Email;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileCreated;
+use Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileId;
+use PHPUnit\Framework\TestCase;
+use Prophecy\PhpUnit\ProphecyTrait;
+
+use function serialize;
+use function unserialize;
+
+#[Attribute(Attribute::TARGET_PROPERTY)]
+final class UnionObjectNormalizerTest extends TestCase
+{
+    use ProphecyTrait;
+
+    public function testNormalizeMissingHydrator(): void
+    {
+        $this->expectException(MissingHydrator::class);
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $this->assertEquals(null, $normalizer->normalize(null));
+    }
+
+    public function testDenormalizeMissingHydrator(): void
+    {
+        $this->expectException(MissingHydrator::class);
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $this->assertEquals(null, $normalizer->denormalize(null));
+    }
+
+    public function testNormalizeWithNull(): void
+    {
+        $hydrator = $this->prophesize(Hydrator::class);
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $normalizer->setHydrator($hydrator->reveal());
+
+        $this->assertEquals(null, $normalizer->normalize(null));
+    }
+
+    public function testDenormalizeWithNull(): void
+    {
+        $hydrator = $this->prophesize(Hydrator::class);
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $normalizer->setHydrator($hydrator->reveal());
+
+        $this->assertEquals(null, $normalizer->denormalize(null));
+    }
+
+    public function testNormalizeWithInvalidArgument(): void
+    {
+        $this->expectException(InvalidArgument::class);
+        $this->expectExceptionMessage('type "Patchlevel\Hydrator\Tests\Unit\Fixture\ProfileCreated|null" was expected but "string" was passed.');
+
+        $hydrator = $this->prophesize(Hydrator::class);
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $normalizer->setHydrator($hydrator->reveal());
+        $normalizer->normalize('foo');
+    }
+
+    public function testDenormalizeWithInvalidArgument(): void
+    {
+        $this->expectException(InvalidArgument::class);
+        $this->expectExceptionMessage('array<string, mixed>|null" was expected but "string" was passed.');
+
+        $hydrator = $this->prophesize(Hydrator::class);
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $normalizer->setHydrator($hydrator->reveal());
+        $normalizer->denormalize('foo');
+    }
+
+    public function testNormalizeWithValue(): void
+    {
+        $hydrator = $this->prophesize(Hydrator::class);
+
+        $event = new ProfileCreated(
+            ProfileId::fromString('1'),
+            Email::fromString('info@patchlevel.de'),
+        );
+
+        $hydrator->extract($event)
+            ->willReturn(['profileId' => '1', 'email' => 'info@patchlevel.de'])
+            ->shouldBeCalledOnce();
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $normalizer->setHydrator($hydrator->reveal());
+
+        self::assertEquals(
+            $normalizer->normalize($event),
+            ['profileId' => '1', 'email' => 'info@patchlevel.de', '_type' => 'created'],
+        );
+    }
+
+    public function testDenormalizeWithValue(): void
+    {
+        $hydrator = $this->prophesize(Hydrator::class);
+
+        $expected = new ProfileCreated(
+            ProfileId::fromString('1'),
+            Email::fromString('info@patchlevel.de'),
+        );
+
+        $hydrator->hydrate(ProfileCreated::class, ['profileId' => '1', 'email' => 'info@patchlevel.de'])
+            ->willReturn($expected)
+            ->shouldBeCalledOnce();
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $normalizer->setHydrator($hydrator->reveal());
+
+        $this->assertEquals(
+            $expected,
+            $normalizer->denormalize(['profileId' => '1', 'email' => 'info@patchlevel.de', '_type' => 'created']),
+        );
+    }
+
+    public function testSerialize(): void
+    {
+        $hydrator = $this->prophesize(Hydrator::class);
+
+        $normalizer = new UnionObjectNormalizer([ProfileCreated::class => 'created']);
+        $normalizer->setHydrator($hydrator->reveal());
+
+        $serialized = serialize($normalizer);
+        $normalizer2 = unserialize($serialized);
+
+        self::assertInstanceOf(UnionObjectNormalizer::class, $normalizer2);
+        self::assertEquals(new UnionObjectNormalizer([ProfileCreated::class => 'created']), $normalizer2);
+    }
+}