diff --git a/src/Attributes/Validation/Sometimes.php b/src/Attributes/Validation/Sometimes.php
new file mode 100644
index 000000000..32fd4ee8b
--- /dev/null
+++ b/src/Attributes/Validation/Sometimes.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Spatie\LaravelData\Attributes\Validation;
+
+use Attribute;
+
+#[Attribute(Attribute::TARGET_PROPERTY)]
+class Sometimes extends ValidationAttribute
+{
+    public function getRules(): array
+    {
+        return ['sometimes'];
+    }
+}
diff --git a/src/Resolvers/DataFromArrayResolver.php b/src/Resolvers/DataFromArrayResolver.php
index f2ea9c0a7..cf4b885cd 100644
--- a/src/Resolvers/DataFromArrayResolver.php
+++ b/src/Resolvers/DataFromArrayResolver.php
@@ -8,6 +8,7 @@
 use Spatie\LaravelData\Lazy;
 use Spatie\LaravelData\Support\DataConfig;
 use Spatie\LaravelData\Support\DataProperty;
+use Spatie\LaravelData\Undefined;
 
 class DataFromArrayResolver
 {
@@ -41,12 +42,16 @@ private function shouldIgnoreProperty(DataProperty $property, array $values): bo
 
     private function resolveValue(DataProperty $property, array $values): mixed
     {
-        $value = $values[$property->name()] ?? null;
+        $value =  array_key_exists($property->name(), $values) ? $values[$property->name()] ?? null : Undefined::make();
 
         if ($value === null) {
             return $value;
         }
 
+        if ($value instanceof Undefined) {
+            return $value;
+        }
+
         if ($value instanceof Lazy) {
             return $value;
         }
diff --git a/src/RuleInferrers/SometimesRuleInferrer.php b/src/RuleInferrers/SometimesRuleInferrer.php
new file mode 100644
index 000000000..2acdd3715
--- /dev/null
+++ b/src/RuleInferrers/SometimesRuleInferrer.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace Spatie\LaravelData\RuleInferrers;
+
+use Spatie\LaravelData\Support\DataProperty;
+
+class SometimesRuleInferrer implements RuleInferrer
+{
+    public function handle(DataProperty $property, array $rules): array
+    {
+        if ($property->isUndefinable() && ! in_array('sometimes', $rules)) {
+            $rules[] = 'sometimes';
+        }
+
+        return $rules;
+    }
+}
diff --git a/src/Support/DataProperty.php b/src/Support/DataProperty.php
index fd9caa3f9..de430ccaa 100644
--- a/src/Support/DataProperty.php
+++ b/src/Support/DataProperty.php
@@ -15,6 +15,7 @@
 use Spatie\LaravelData\Exceptions\CannotFindDataTypeForProperty;
 use Spatie\LaravelData\Exceptions\InvalidDataPropertyType;
 use Spatie\LaravelData\Lazy;
+use Spatie\LaravelData\Undefined;
 use TypeError;
 
 class DataProperty
@@ -23,6 +24,8 @@ class DataProperty
 
     protected bool $isNullable;
 
+    protected bool $isUndefinable;
+
     protected bool $isData;
 
     protected bool $isDataCollection;
@@ -75,6 +78,11 @@ public function isNullable(): bool
         return $this->isNullable;
     }
 
+    public function isUndefinable(): bool
+    {
+        return $this->isUndefinable;
+    }
+
     public function isPromoted(): bool
     {
         return $this->property->isPromoted();
@@ -177,6 +185,7 @@ private function processNoType(): void
     {
         $this->isLazy = false;
         $this->isNullable = true;
+        $this->isUndefinable = false;
         $this->isData = false;
         $this->isDataCollection = false;
         $this->types = new DataPropertyTypes();
@@ -194,6 +203,7 @@ private function processNamedType(ReflectionNamedType $type)
         $this->isData = is_a($name, Data::class, true);
         $this->isDataCollection = is_a($name, DataCollection::class, true);
         $this->isNullable = $type->allowsNull();
+        $this->isUndefinable = is_a($name, Undefined::class, true);
         $this->types = new DataPropertyTypes([$name]);
     }
 
@@ -201,6 +211,7 @@ private function processListType(ReflectionUnionType|ReflectionIntersectionType
     {
         $this->isLazy = false;
         $this->isNullable = false;
+        $this->isUndefinable = false;
         $this->isData = false;
         $this->isDataCollection = false;
         $this->types = new DataPropertyTypes();
@@ -214,6 +225,12 @@ private function processListType(ReflectionUnionType|ReflectionIntersectionType
                 continue;
             }
 
+            if ($name === Undefined::class) {
+                $this->isUndefinable = true;
+
+                continue;
+            }
+
             if ($name === Lazy::class) {
                 $this->isLazy = true;
 
diff --git a/src/Support/TypeScriptTransformer/DataTypeScriptTransformer.php b/src/Support/TypeScriptTransformer/DataTypeScriptTransformer.php
index e43740cdc..0c5b208d0 100644
--- a/src/Support/TypeScriptTransformer/DataTypeScriptTransformer.php
+++ b/src/Support/TypeScriptTransformer/DataTypeScriptTransformer.php
@@ -27,6 +27,7 @@ protected function typeProcessors(): array
                 $this->config->getDefaultTypeReplacements()
             ),
             new RemoveLazyTypeProcessor(),
+            new RemoveUndefinedTypeProcessor(),
             new DtoCollectionTypeProcessor(),
         ];
     }
diff --git a/src/Support/TypeScriptTransformer/RemoveUndefinedTypeProcessor.php b/src/Support/TypeScriptTransformer/RemoveUndefinedTypeProcessor.php
new file mode 100644
index 000000000..cf6a06246
--- /dev/null
+++ b/src/Support/TypeScriptTransformer/RemoveUndefinedTypeProcessor.php
@@ -0,0 +1,48 @@
+<?php
+
+namespace Spatie\LaravelData\Support\TypeScriptTransformer;
+
+use Exception;
+use phpDocumentor\Reflection\Type;
+use phpDocumentor\Reflection\Types\Compound;
+use phpDocumentor\Reflection\Types\Object_;
+use ReflectionMethod;
+use ReflectionParameter;
+use ReflectionProperty;
+use Spatie\LaravelData\Lazy;
+use Spatie\LaravelData\Undefined;
+use Spatie\TypeScriptTransformer\Structures\MissingSymbolsCollection;
+use Spatie\TypeScriptTransformer\TypeProcessors\TypeProcessor;
+
+class RemoveUndefinedTypeProcessor implements TypeProcessor
+{
+    public function process(
+        Type $type,
+        ReflectionParameter | ReflectionMethod | ReflectionProperty $reflection,
+        MissingSymbolsCollection $missingSymbolsCollection
+    ): ?Type {
+        if (! $type instanceof Compound) {
+            return $type;
+        }
+
+        /** @var \Illuminate\Support\Collection $types */
+        $types = collect(iterator_to_array($type->getIterator()))
+            ->reject(function (Type $type) {
+                if (! $type instanceof Object_) {
+                    return false;
+                }
+
+                return is_a((string)$type->getFqsen(), Undefined::class, true);
+            });
+
+        if ($types->isEmpty()) {
+            throw new Exception("Type {$reflection->getDeclaringClass()->name}:{$reflection->getName()} cannot be only Undefined");
+        }
+
+        if ($types->count() === 1) {
+            return $types->first();
+        }
+
+        return new Compound($types->all());
+    }
+}
diff --git a/src/Transformers/DataTransformer.php b/src/Transformers/DataTransformer.php
index 1d673a18b..279f0f60b 100644
--- a/src/Transformers/DataTransformer.php
+++ b/src/Transformers/DataTransformer.php
@@ -8,6 +8,7 @@
 use Spatie\LaravelData\Support\DataConfig;
 use Spatie\LaravelData\Support\DataProperty;
 use Spatie\LaravelData\Support\TransformationType;
+use Spatie\LaravelData\Undefined;
 
 class DataTransformer
 {
@@ -71,6 +72,10 @@ protected function shouldIncludeProperty(
         ?array $allowedIncludes,
         ?array $allowedExcludes,
     ): bool {
+        if ($value instanceof Undefined) {
+            return false;
+        }
+
         if (! $value instanceof Lazy) {
             return true;
         }
diff --git a/src/Undefined.php b/src/Undefined.php
new file mode 100644
index 000000000..dd4edf505
--- /dev/null
+++ b/src/Undefined.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Spatie\LaravelData;
+
+
+class Undefined
+{
+    public static function make(): Undefined
+    {
+        return new self();
+    }
+}
diff --git a/tests/Attributes/Validation/RulesTest.php b/tests/Attributes/Validation/RulesTest.php
index 337a70cd2..ff8352c40 100644
--- a/tests/Attributes/Validation/RulesTest.php
+++ b/tests/Attributes/Validation/RulesTest.php
@@ -82,6 +82,7 @@
 use Spatie\LaravelData\Attributes\Validation\Rule;
 use Spatie\LaravelData\Attributes\Validation\Same;
 use Spatie\LaravelData\Attributes\Validation\Size;
+use Spatie\LaravelData\Attributes\Validation\Sometimes;
 use Spatie\LaravelData\Attributes\Validation\StartsWith;
 use Spatie\LaravelData\Attributes\Validation\StringType;
 use Spatie\LaravelData\Attributes\Validation\Timezone;
@@ -373,6 +374,11 @@ public function attributesDataProvider(): Generator
             'attribute' => new Uuid(),
             'expected' => ['uuid'],
         ];
+
+        yield [
+            'attribute' => new Sometimes(),
+            'expected' => ['sometimes'],
+        ];
     }
 
     public function acceptedIfAttributesDataProvider(): Generator
diff --git a/tests/DataTest.php b/tests/DataTest.php
index c1fb1a7e8..b09f0272f 100644
--- a/tests/DataTest.php
+++ b/tests/DataTest.php
@@ -17,6 +17,7 @@
 use Spatie\LaravelData\Tests\Factories\DataBlueprintFactory;
 use Spatie\LaravelData\Tests\Factories\DataPropertyBlueprintFactory;
 use Spatie\LaravelData\Tests\Fakes\DefaultLazyData;
+use Spatie\LaravelData\Tests\Fakes\DefaultUndefinedData;
 use Spatie\LaravelData\Tests\Fakes\DummyDto;
 use Spatie\LaravelData\Tests\Fakes\DummyModel;
 use Spatie\LaravelData\Tests\Fakes\DummyModelWithCasts;
@@ -773,4 +774,25 @@ public function it_can_construct_a_data_object_with_default_values_and_overwrite
         $this->assertEquals('Test', $data->default_property);
         $this->assertEquals('Test Again', $data->default_promoted_property);
     }
+
+
+    /** @test */
+    public function it_excludes_undefined_values_data()
+    {
+        $data = DefaultUndefinedData::from([]);
+
+        $this->assertEquals([], $data->toArray());
+    }
+
+    /** @test */
+    public function it_includes_value_if_not_undefined_data()
+    {
+        $data = DefaultUndefinedData::from([
+            'name' => 'Freek'
+        ]);
+
+        $this->assertEquals([
+            'name' => 'Freek'
+        ], $data->toArray());
+    }
 }
diff --git a/tests/Fakes/ComplicatedData.php b/tests/Fakes/ComplicatedData.php
index 74bed5a8c..3693b8b2a 100644
--- a/tests/Fakes/ComplicatedData.php
+++ b/tests/Fakes/ComplicatedData.php
@@ -8,6 +8,7 @@
 use Spatie\LaravelData\Casts\DateTimeInterfaceCast;
 use Spatie\LaravelData\Data;
 use Spatie\LaravelData\DataCollection;
+use Spatie\LaravelData\Undefined;
 
 class ComplicatedData extends Data
 {
@@ -19,6 +20,7 @@ public function __construct(
         public string $string,
         public array $array,
         public ?int $nullable,
+        public int|Undefined $undefinable,
         public mixed $mixed,
         #[WithCast(DateTimeInterfaceCast::class, format: 'd-m-Y', type: CarbonImmutable::class)]
         public $explicitCast,
diff --git a/tests/Fakes/DefaultUndefinedData.php b/tests/Fakes/DefaultUndefinedData.php
new file mode 100644
index 000000000..5c6481787
--- /dev/null
+++ b/tests/Fakes/DefaultUndefinedData.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Spatie\LaravelData\Tests\Fakes;
+
+use Spatie\LaravelData\Data;
+use Spatie\LaravelData\Undefined;
+
+class DefaultUndefinedData extends Data
+{
+    public function __construct(
+        public string | Undefined $name
+    ) {
+    }
+}
diff --git a/tests/Resolvers/DataFromArrayResolverTest.php b/tests/Resolvers/DataFromArrayResolverTest.php
index 6dd4debad..f649dc2e7 100644
--- a/tests/Resolvers/DataFromArrayResolverTest.php
+++ b/tests/Resolvers/DataFromArrayResolverTest.php
@@ -19,6 +19,7 @@
 use Spatie\LaravelData\Tests\Fakes\NestedModelData;
 use Spatie\LaravelData\Tests\Fakes\SimpleData;
 use Spatie\LaravelData\Tests\TestCase;
+use Spatie\LaravelData\Undefined;
 
 class DataFromArrayResolverTest extends TestCase
 {
@@ -69,6 +70,7 @@ public function it_maps_default_types()
         $this->assertEquals('Hello world', $data->string);
         $this->assertEquals([1, 1, 2, 3, 5, 8], $data->array);
         $this->assertNull($data->nullable);
+        $this->assertInstanceOf(Undefined::class, $data->undefinable);
         $this->assertEquals(42, $data->mixed);
         $this->assertEquals(DateTime::createFromFormat(DATE_ATOM, '1994-05-16T12:00:00+01:00'), $data->defaultCast);
         $this->assertEquals(CarbonImmutable::createFromFormat('d-m-Y', '16-06-1994'), $data->explicitCast);
diff --git a/tests/Resolvers/EmptyDataResolverTest.php b/tests/Resolvers/EmptyDataResolverTest.php
index bee466b74..b480d6312 100644
--- a/tests/Resolvers/EmptyDataResolverTest.php
+++ b/tests/Resolvers/EmptyDataResolverTest.php
@@ -10,6 +10,7 @@
 use Spatie\LaravelData\Resolvers\EmptyDataResolver;
 use Spatie\LaravelData\Tests\Fakes\SimpleData;
 use Spatie\LaravelData\Tests\TestCase;
+use Spatie\LaravelData\Undefined;
 
 class EmptyDataResolverTest extends TestCase
 {
@@ -105,6 +106,37 @@ public function it_will_return_the_base_type_for_lazy_types_that_can_be_null()
         });
     }
 
+    public function it_will_return_the_base_type_for_lazy_types_that_can_be_undefined()
+    {
+        $this->assertEmptyPropertyValue(null, new class () {
+            public Lazy | string | Undefined $property;
+        });
+
+        $this->assertEmptyPropertyValue([], new class () {
+            public Lazy | array | Undefined $property;
+        });
+
+        $this->assertEmptyPropertyValue(['string' => null], new class () {
+            public Lazy | SimpleData | Undefined $property;
+        });
+    }
+
+    /** @test */
+    public function it_will_return_the_base_type_for_undefinable_types()
+    {
+        $this->assertEmptyPropertyValue(null, new class() {
+            public Undefined | string $property;
+        });
+
+        $this->assertEmptyPropertyValue([], new class () {
+            public Undefined | array $property;
+        });
+
+        $this->assertEmptyPropertyValue(['string' => null], new class () {
+            public Undefined | SimpleData $property;
+        });
+    }
+
     /** @test */
     public function it_cannot_have_multiple_types()
     {
@@ -135,6 +167,26 @@ public function it_cannot_have_multiple_types_with_a_nullable_lazy()
         });
     }
 
+    /** @test */
+    public function it_cannot_have_multiple_types_with_a_undefined()
+    {
+        $this->expectException(DataPropertyCanOnlyHaveOneType::class);
+
+        $this->assertEmptyPropertyValue(null, new class () {
+            public int | string | Undefined $property;
+        });
+    }
+
+    /** @test */
+    public function it_cannot_have_multiple_types_with_a_nullable_undefined()
+    {
+        $this->expectException(DataPropertyCanOnlyHaveOneType::class);
+
+        $this->assertEmptyPropertyValue(null, new class () {
+            public int | string | Undefined | null $property;
+        });
+    }
+
     /** @test */
     public function it_can_overwrite_empty_properties()
     {
diff --git a/tests/Support/DataPropertyTest.php b/tests/Support/DataPropertyTest.php
index 2538a4fe4..b5e147a1f 100644
--- a/tests/Support/DataPropertyTest.php
+++ b/tests/Support/DataPropertyTest.php
@@ -21,6 +21,7 @@
 use Spatie\LaravelData\Tests\Fakes\SimpleData;
 use Spatie\LaravelData\Tests\TestCase;
 use Spatie\LaravelData\Transformers\DateTimeInterfaceTransformer;
+use Spatie\LaravelData\Undefined;
 
 class DataPropertyTest extends TestCase
 {
@@ -33,6 +34,7 @@ public function it_works_with_non_typed_properties()
 
         $this->assertFalse($helper->isLazy());
         $this->assertTrue($helper->isNullable());
+        $this->assertFalse($helper->isUndefinable());
         $this->assertFalse($helper->isData());
         $this->assertFalse($helper->isDataCollection());
         $this->assertTrue($helper->types()->isEmpty());
@@ -84,6 +86,29 @@ public function it_can_check_if_a_property_is_nullable()
         $this->assertTrue($helper->isNullable());
     }
 
+    /** @test */
+    public function it_can_check_if_a_property_is_undefinable()
+    {
+        $helper = $this->resolveHelper(new class () {
+            public int $property;
+        });
+
+        $this->assertFalse($helper->isUndefinable());
+
+        $helper = $this->resolveHelper(new class () {
+            public Undefined $property;
+        });
+
+        $this->assertTrue($helper->isUndefinable());
+
+        $helper = $this->resolveHelper(new class () {
+            public Undefined|int $property;
+        });
+
+        $this->assertTrue($helper->isUndefinable());
+    }
+
+
     /** @test */
     public function it_can_check_if_a_property_is_a_data_object()
     {
diff --git a/tests/Support/TypeScriptTransformer/DataTypeScriptTransformerTest.php b/tests/Support/TypeScriptTransformer/DataTypeScriptTransformerTest.php
index 4f8cfb762..7e5213276 100644
--- a/tests/Support/TypeScriptTransformer/DataTypeScriptTransformerTest.php
+++ b/tests/Support/TypeScriptTransformer/DataTypeScriptTransformerTest.php
@@ -9,6 +9,7 @@
 use Spatie\LaravelData\Support\TypeScriptTransformer\DataTypeScriptTransformer;
 use Spatie\LaravelData\Tests\Fakes\SimpleData;
 use Spatie\LaravelData\Tests\TestCase;
+use Spatie\LaravelData\Undefined;
 use Spatie\TypeScriptTransformer\TypeScriptTransformerConfig;
 
 class DataTypeScriptTransformerTest extends TestCase
@@ -18,9 +19,12 @@ public function it_can_covert_a_data_object_to_typescript()
     {
         $config = TypeScriptTransformerConfig::create();
 
-        $data = new class (null, 42, true, 'Hello world', 3.14, ['the', 'meaning', 'of', 'life'], Lazy::create(fn () => 'Lazy'), SimpleData::from('Simple data'), SimpleData::collection([]), ) extends Data {
+        $data = new class (null, Undefined::make(), 42, true, 'Hello world', 3.14, ['the', 'meaning', 'of', 'life'],
+            Lazy::create(fn
+        () => 'Lazy'), SimpleData::from('Simple data'), SimpleData::collection([]), ) extends Data {
             public function __construct(
                 public null | int $nullable,
+                public Undefined | int $undefineable,
                 public int $int,
                 public bool $bool,
                 public string $string,
diff --git a/tests/Support/TypeScriptTransformer/__snapshots__/DataTypeScriptTransformerTest__it_can_covert_a_data_object_to_typescript__1.txt b/tests/Support/TypeScriptTransformer/__snapshots__/DataTypeScriptTransformerTest__it_can_covert_a_data_object_to_typescript__1.txt
index 4cf1f171d..6084c05d7 100644
--- a/tests/Support/TypeScriptTransformer/__snapshots__/DataTypeScriptTransformerTest__it_can_covert_a_data_object_to_typescript__1.txt
+++ b/tests/Support/TypeScriptTransformer/__snapshots__/DataTypeScriptTransformerTest__it_can_covert_a_data_object_to_typescript__1.txt
@@ -1,5 +1,6 @@
 {
 nullable: number | null;
+undefineable: number;
 int: number;
 bool: boolean;
 string: string;