diff --git a/src/implementation/flags/EvaluationDetails.php b/src/implementation/flags/EvaluationDetails.php
index d96c46b..744b21b 100644
--- a/src/implementation/flags/EvaluationDetails.php
+++ b/src/implementation/flags/EvaluationDetails.php
@@ -8,6 +8,8 @@
 use OpenFeature\interfaces\flags\EvaluationDetails as EvaluationDetailsInterface;
 use OpenFeature\interfaces\provider\ResolutionError;
 
+use function is_array;
+
 class EvaluationDetails implements EvaluationDetailsInterface
 {
     private string $flagKey = '';
@@ -17,6 +19,8 @@ class EvaluationDetails implements EvaluationDetailsInterface
     private ?ResolutionError $error = null;
     private ?string $reason = null;
     private ?string $variant = null;
+    /** @var array<string,bool|string|int|float>|null $metadata */
+    private ?array $metadata = null;
 
     public function __construct()
     {
@@ -83,4 +87,36 @@ public function setVariant(?string $variant): void
     {
         $this->variant = $variant;
     }
+
+    /**
+     * @param array<string,bool|string|int|float>|null $metadata
+     */
+    public function setMetadata(?array $metadata): void
+    {
+        if (is_array($metadata)) {
+            $this->metadata = [];
+            foreach ($metadata as $key => $value) {
+                $this->metadata[$key] = $value;
+            }
+        } else {
+            $this->metadata = null;
+        }
+    }
+
+    /**
+     * @return array<string,bool|string|int|float>
+     */
+    public function getMetadata(): array
+    {
+        if ($this->metadata === null) {
+            return [];
+        }
+        /** @var array<string,bool|string|int|float> $metadata */
+        $metadata = [];
+        foreach ($this->metadata as $key => $value) {
+            $metadata[$key] = $value;
+        }
+
+        return $metadata;
+    }
 }
diff --git a/src/implementation/flags/EvaluationDetailsBuilder.php b/src/implementation/flags/EvaluationDetailsBuilder.php
index 7cb4dc6..ce2a45d 100644
--- a/src/implementation/flags/EvaluationDetailsBuilder.php
+++ b/src/implementation/flags/EvaluationDetailsBuilder.php
@@ -55,6 +55,16 @@ public function withVariant(?string $variant): EvaluationDetailsBuilder
         return $this;
     }
 
+    /**
+     * @param array<string,bool|string|int|float>|null $metadata
+     */
+    public function withMetadata(?array $metadata): EvaluationDetailsBuilder
+    {
+        $this->details->setMetadata($metadata);
+
+        return $this;
+    }
+
     public function build(): EvaluationDetailsInterface
     {
         return $this->details;
diff --git a/src/implementation/flags/EvaluationDetailsFactory.php b/src/implementation/flags/EvaluationDetailsFactory.php
index 6115799..a48b3c7 100644
--- a/src/implementation/flags/EvaluationDetailsFactory.php
+++ b/src/implementation/flags/EvaluationDetailsFactory.php
@@ -34,6 +34,7 @@ public static function fromResolution(string $flagKey, ResolutionDetails $detail
                     ->withError($details->getError())
                     ->withReason($details->getReason())
                     ->withVariant($details->getVariant())
+                    ->withMetadata($details->getMetadata())
                     ->build();
     }
 }
diff --git a/src/implementation/provider/ResolutionDetails.php b/src/implementation/provider/ResolutionDetails.php
index 29750d9..1f015f3 100644
--- a/src/implementation/provider/ResolutionDetails.php
+++ b/src/implementation/provider/ResolutionDetails.php
@@ -8,6 +8,8 @@
 use OpenFeature\interfaces\provider\ResolutionDetails as ResolutionDetailsInterface;
 use OpenFeature\interfaces\provider\ResolutionError;
 
+use function is_array;
+
 class ResolutionDetails implements ResolutionDetailsInterface
 {
     /** @var bool|string|int|float|DateTime|mixed[]|null $value */
@@ -15,6 +17,8 @@ class ResolutionDetails implements ResolutionDetailsInterface
     private ?ResolutionError $error = null;
     private ?string $reason = null;
     private ?string $variant = null;
+    /** @var array<string,bool|string|int|float>|null $metadata */
+    private ?array $metadata = null;
 
     /**
      * @return bool|string|int|float|DateTime|mixed[]|null
@@ -61,4 +65,36 @@ public function setVariant(?string $variant): void
     {
         $this->variant = $variant;
     }
+
+    /**
+     * @param array<string,bool|string|int|float>|null $metadata
+     */
+    public function setMetadata(?array $metadata): void
+    {
+        if (is_array($metadata)) {
+            $this->metadata = [];
+            foreach ($metadata as $key => $value) {
+                $this->metadata[$key] = $value;
+            }
+        } else {
+            $this->metadata = null;
+        }
+    }
+
+    /**
+     * @return array<string,bool|string|int|float>|null
+     */
+    public function getMetadata(): ?array
+    {
+        if ($this->metadata === null) {
+            return null;
+        }
+        /** @var array<string,bool|string|int|float> $metadata */
+        $metadata = [];
+        foreach ($this->metadata as $key => $value) {
+            $metadata[$key] = $value;
+        }
+
+        return $metadata;
+    }
 }
diff --git a/src/implementation/provider/ResolutionDetailsBuilder.php b/src/implementation/provider/ResolutionDetailsBuilder.php
index 73ae2c7..45579fa 100644
--- a/src/implementation/provider/ResolutionDetailsBuilder.php
+++ b/src/implementation/provider/ResolutionDetailsBuilder.php
@@ -48,6 +48,16 @@ public function withVariant(string $variant): ResolutionDetailsBuilder
         return $this;
     }
 
+    /**
+     * @param array<string,bool|string|int|float>|null $metadata
+     */
+    public function withMetadata(?array $metadata): ResolutionDetailsBuilder
+    {
+        $this->details->setMetadata($metadata);
+
+        return $this;
+    }
+
     public function build(): ResolutionDetailsInterface
     {
         return $this->details;
diff --git a/src/interfaces/flags/EvaluationDetails.php b/src/interfaces/flags/EvaluationDetails.php
index 4dd269e..7af0f51 100644
--- a/src/interfaces/flags/EvaluationDetails.php
+++ b/src/interfaces/flags/EvaluationDetails.php
@@ -64,4 +64,16 @@ public function getReason(): ?string;
      * the configured provider, if the field is set.
      */
     public function getVariant(): ?string;
+
+    /**
+     * ------------------
+     * Requirement 1.4.14
+     * ------------------
+     * If the flag metadata field in the flag resolution structure returned by the configured
+     * provider is set, the evaluation details structure's flag metadata field MUST contain that
+     * value. Otherwise, it MUST contain an empty record.
+     *
+     * @return array<string,bool|string|int|float>
+     */
+    public function getMetadata(): array;
 }
diff --git a/src/interfaces/provider/ResolutionDetails.php b/src/interfaces/provider/ResolutionDetails.php
index c50edb2..64a2d42 100644
--- a/src/interfaces/provider/ResolutionDetails.php
+++ b/src/interfaces/provider/ResolutionDetails.php
@@ -51,4 +51,14 @@ public function getReason(): ?string;
      * with a string identifier corresponding to the returned flag value.
      */
     public function getVariant(): ?string;
+
+    /**
+     * -----------------
+     * Requirement 2.2.9
+     * -----------------
+     * The provider SHOULD populate the resolution details structure's flag metadata field.
+     *
+     * @return array<string,bool|string|int|float>|null
+     */
+    public function getMetadata(): ?array;
 }
diff --git a/tests/unit/EvaluationDetailsMetadataTest.php b/tests/unit/EvaluationDetailsMetadataTest.php
new file mode 100644
index 0000000..aa370b2
--- /dev/null
+++ b/tests/unit/EvaluationDetailsMetadataTest.php
@@ -0,0 +1,134 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenFeature\Test\unit;
+
+use DateTime;
+use Mockery;
+use Mockery\MockInterface;
+use OpenFeature\Test\TestCase;
+use OpenFeature\implementation\flags\EvaluationDetailsBuilder;
+use OpenFeature\implementation\flags\EvaluationDetailsFactory;
+use OpenFeature\implementation\provider\ResolutionDetailsBuilder;
+use OpenFeature\interfaces\flags\EvaluationDetails;
+use OpenFeature\interfaces\provider\Provider;
+use OpenFeature\interfaces\provider\ResolutionDetails;
+
+class EvaluationDetailsMetadataTest extends TestCase
+{
+    /** @var Provider&MockInterface */
+    private Provider $provider;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->provider = Mockery::mock(Provider::class);
+        $this->provider->shouldReceive('getMetadata->getName')->andReturn('TestProvider');
+    }
+
+    /**
+     * @param bool|string|int|float|DateTime|array<mixed>|null $value
+     */
+    private function details(bool | string | int | float | DateTime | array | null $value): EvaluationDetails
+    {
+        return (new EvaluationDetailsBuilder())->withValue($value)->build();
+    }
+
+    /**
+     * @param bool|string|int|float|DateTime|array<mixed>|null $value
+     * @param array<string,bool|string|int> $metadata
+     */
+    private function detailsWithMetadata(bool | string | int | float | DateTime | array | null $value, array $metadata): EvaluationDetails
+    {
+        return (new EvaluationDetailsBuilder())->withValue($value)->withMetadata($metadata)->build();
+    }
+
+    /**
+     * @param bool|string|int|float|DateTime|array<mixed>|null $value
+     */
+    private function resolution(bool | string | int | float | DateTime | array | null $value): ResolutionDetails
+    {
+        return (new ResolutionDetailsBuilder())->withValue($value)->build();
+    }
+
+    /**
+     * @param bool|string|int|float|DateTime|array<mixed>|null $value
+     * @param array<string,bool|string|int> $metadata
+     */
+    private function resolutionWithMetadata(bool | string | int | float | DateTime | array | null $value, array $metadata): ResolutionDetails
+    {
+        return (new ResolutionDetailsBuilder())->withValue($value)->withMetadata($metadata)->build();
+    }
+
+    public function testEvaluationResultWithEmptyMetadata(): void
+    {
+        $details = $this->details(true);
+        $metadata = $details->getMetadata();
+        $this->assertNotNull($metadata);
+        $this->assertIsArray($metadata);
+        $this->assertEmpty($metadata);
+    }
+
+    public function testEvaluationResultWithNotEmptyMetadata(): void
+    {
+        $details = $this->detailsWithMetadata(true, [
+            'bool_value' => true,
+            'string_value' => 'OK',
+        ]);
+        $metadata = $details->getMetadata();
+        $this->assertNotNull($metadata);
+        $this->assertIsArray($metadata);
+        $this->assertNotEmpty($metadata);
+        $this->assertArrayHasKey('bool_value', $metadata);
+        $this->assertArrayHasKey('string_value', $metadata);
+        $this->assertEquals(true, $metadata['bool_value']);
+        $this->assertEquals('OK', $metadata['string_value']);
+    }
+
+    public function testEvaluationResultMetadataImmutability(): void
+    {
+        $details = $this->detailsWithMetadata(true, [
+            'bool_value' => true,
+            'string_value' => 'OK',
+        ]);
+        $metadata = $details->getMetadata();
+        // let's add a new key/value and let's change the value of "bool_value"
+        $metadata['number_value'] = 7;
+        $metadata['bool_value'] = false;
+        // get again the metadata
+        $newMetadata = $details->getMetadata();
+
+        $this->assertNotSame($metadata, $newMetadata);
+        $this->assertArrayNotHasKey('number_value', $newMetadata);
+        $this->assertArrayHasKey('bool_value', $newMetadata);
+        $this->assertNotEquals(false, $newMetadata['bool_value']);
+        $this->assertNotSameSize($metadata, $newMetadata);
+    }
+
+    public function testEvaluationDetailsFromResolutionDetailsWithoutMetadata(): void
+    {
+        $resolution = $this->resolution(true);
+        $details = EvaluationDetailsFactory::fromResolution('test-key', $resolution);
+
+        $this->assertNull($resolution->getMetadata());
+        $this->assertNotNull($details->getMetadata());
+        $this->assertIsArray($details->getMetadata());
+        $this->assertEmpty($details->getMetadata());
+        $this->assertNotSame($resolution->getMetadata(), $details->getMetadata());
+    }
+
+    public function testEvaluationDetailsFromResolutionDetailsWithMetadata(): void
+    {
+        $resolution = $this->resolutionWithMetadata(true, [
+            'key' => 'value',
+        ]);
+        $details = EvaluationDetailsFactory::fromResolution('test-key', $resolution);
+
+        $this->assertNotNull($resolution->getMetadata());
+        $this->assertNotNull($details->getMetadata());
+        $this->assertIsArray($details->getMetadata());
+        $this->assertNotEmpty($details->getMetadata());
+        $this->assertArrayHasKey('key', $details->getMetadata());
+    }
+}
diff --git a/tests/unit/ProviderResolutionResultTest.php b/tests/unit/ProviderResolutionResultTest.php
index 577fc7d..021f7ec 100644
--- a/tests/unit/ProviderResolutionResultTest.php
+++ b/tests/unit/ProviderResolutionResultTest.php
@@ -34,6 +34,15 @@ private function details(bool | string | int | float | DateTime | array | null $
         return (new ResolutionDetailsBuilder())->withValue($value)->build();
     }
 
+    /**
+     * @param bool|string|int|float|DateTime|array<mixed>|null $value
+     * @param array<string,bool|string|int>|null $metadata
+     */
+    private function detailsWithMetadata(bool | string | int | float | DateTime | array | null $value, ?array $metadata): ResolutionDetails
+    {
+        return (new ResolutionDetailsBuilder())->withValue($value)->withMetadata($metadata)->build();
+    }
+
     public function testSuccessfulResult(): void
     {
         $details = $this->details(true);
@@ -68,4 +77,52 @@ public function testEmptyResultNeitherSuccessNorError(): void
         $this->assertFalse($result->hasError());
         $this->assertFalse($result->isSuccessful());
     }
+
+    public function testResultWithNotEmptyMetadata(): void
+    {
+        $details = $this->detailsWithMetadata(true, [
+            'test_bool' => true,
+            'test_int' => 10,
+            'test_string' => 'OK',
+        ]);
+        $result = new ProviderResolutionResult('TestProvider', $this->provider, $details, null);
+
+        $this->assertSame($details, $result->getDetails());
+        $this->assertNull($result->getError());
+        $this->assertFalse($result->hasError());
+        $this->assertTrue($result->isSuccessful());
+        $this->assertIsArray($details->getMetadata());
+        $this->assertArrayHasKey('test_bool', $details->getMetadata());
+        $this->assertArrayHasKey('test_int', $details->getMetadata());
+        $this->assertArrayHasKey('test_string', $details->getMetadata());
+        $this->assertEquals(true, $details->getMetadata()['test_bool']);
+        $this->assertEquals('OK', $details->getMetadata()['test_string']);
+        $this->assertEquals(10, $details->getMetadata()['test_int']);
+    }
+
+    public function testResultWithEmptyMetadata(): void
+    {
+        $details = $this->detailsWithMetadata(true, []);
+        $result = new ProviderResolutionResult('TestProvider', $this->provider, $details, null);
+
+        $this->assertSame($details, $result->getDetails());
+        $this->assertNull($result->getError());
+        $this->assertFalse($result->hasError());
+        $this->assertTrue($result->isSuccessful());
+        $this->assertIsArray($details->getMetadata());
+        $this->assertSame([], $details->getMetadata());
+    }
+
+    public function testResultWithNullMetadata(): void
+    {
+        $details = $this->detailsWithMetadata(true, null);
+        $result = new ProviderResolutionResult('TestProvider', $this->provider, $details, null);
+
+        $this->assertSame($details, $result->getDetails());
+        $this->assertNull($result->getError());
+        $this->assertFalse($result->hasError());
+        $this->assertTrue($result->isSuccessful());
+        $this->assertNull($details->getMetadata());
+        $this->assertIsNotArray($details->getMetadata());
+    }
 }
diff --git a/tests/unit/ResolutionDetailsMetadataTest.php b/tests/unit/ResolutionDetailsMetadataTest.php
new file mode 100644
index 0000000..0cb5bbb
--- /dev/null
+++ b/tests/unit/ResolutionDetailsMetadataTest.php
@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenFeature\Test\unit;
+
+use DateTime;
+use Mockery;
+use Mockery\MockInterface;
+use OpenFeature\Test\TestCase;
+use OpenFeature\implementation\provider\ResolutionDetailsBuilder;
+use OpenFeature\interfaces\provider\Provider;
+use OpenFeature\interfaces\provider\ResolutionDetails;
+
+class ResolutionDetailsMetadataTest extends TestCase
+{
+    /** @var Provider&MockInterface */
+    private Provider $provider;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->provider = Mockery::mock(Provider::class);
+        $this->provider->shouldReceive('getMetadata->getName')->andReturn('TestProvider');
+    }
+
+    /**
+     * @param bool|string|int|float|DateTime|array<mixed>|null $value
+     */
+    private function details(bool | string | int | float | DateTime | array | null $value): ResolutionDetails
+    {
+        return (new ResolutionDetailsBuilder())->withValue($value)->build();
+    }
+
+    /**
+     * @param bool|string|int|float|DateTime|array<mixed>|null $value
+     * @param array<string,bool|string|int> $metadata
+     */
+    private function detailsWithMetadata(bool | string | int | float | DateTime | array | null $value, array $metadata): ResolutionDetails
+    {
+        return (new ResolutionDetailsBuilder())->withValue($value)->withMetadata($metadata)->build();
+    }
+
+    public function testResolutionDetailsWithoutMetadata(): void
+    {
+        $details = $this->details(true);
+        $this->assertNull($details->getMetadata());
+    }
+
+    public function testResolutionDetailsWithEmptyMetadata(): void
+    {
+        $details = $this->detailsWithMetadata(true, []);
+        $metadata = $details->getMetadata();
+        $this->assertNotNull($metadata);
+        $this->assertIsArray($metadata);
+        $this->assertEmpty($metadata);
+    }
+
+    public function testResolutionDetailsWithNotEmptyMetadata(): void
+    {
+        $details = $this->detailsWithMetadata(true, [
+            'bool_value' => true,
+            'string_value' => 'OK',
+        ]);
+        $metadata = $details->getMetadata();
+        $this->assertNotNull($metadata);
+        $this->assertIsArray($metadata);
+        $this->assertNotEmpty($metadata);
+        $this->assertArrayHasKey('bool_value', $metadata);
+        $this->assertArrayHasKey('string_value', $metadata);
+        $this->assertEquals(true, $metadata['bool_value']);
+        $this->assertEquals('OK', $metadata['string_value']);
+    }
+
+    public function testResolutionDetailsMetadataImmutability(): void
+    {
+        $details = $this->detailsWithMetadata(true, [
+            'bool_value' => true,
+            'string_value' => 'OK',
+        ]);
+        $metadata = $details->getMetadata();
+        // let's add a new key/value and let's change the value of "bool_value"
+        $metadata['number_value'] = 7;
+        $metadata['bool_value'] = false;
+        // get again the metadata
+        $newMetadata = $details->getMetadata();
+
+        $this->assertNotSame($metadata, $newMetadata);
+        $this->assertIsArray($newMetadata);
+        $this->assertArrayNotHasKey('number_value', $newMetadata);
+        $this->assertArrayHasKey('bool_value', $newMetadata);
+        $this->assertNotEquals(false, $newMetadata['bool_value']);
+        $this->assertNotSameSize($metadata, $newMetadata);
+    }
+}