diff --git a/src/JsonSchema/ConstraintError.php b/src/JsonSchema/ConstraintError.php
index 081e38ad..07b489a9 100644
--- a/src/JsonSchema/ConstraintError.php
+++ b/src/JsonSchema/ConstraintError.php
@@ -60,6 +60,7 @@ class ConstraintError extends Enum
     public const PROPERTY_NAMES = 'propertyNames';
     public const TYPE = 'type';
     public const UNIQUE_ITEMS = 'uniqueItems';
+    public const UNEVALUATED_PROPERTIES = 'unevaluatedProperties';
     public const CONTENT_MEDIA_TYPE = 'contentMediaType';
     public const CONTENT_ENCODING = 'contentEncoding';
 
@@ -122,6 +123,7 @@ public function getMessage()
             self::PROPERTY_NAMES => 'Property name %s is invalid',
             self::TYPE => '%s value found, but %s is required',
             self::UNIQUE_ITEMS => 'There are no duplicates allowed in the array',
+            self::UNEVALUATED_PROPERTIES => 'The property %s is not evaluated and the definition does not allow unevaluated properties',
             self::CONTENT_MEDIA_TYPE => 'Value is not valid with content media type',
             self::CONTENT_ENCODING => 'Value is not valid with content encoding',
         ];
diff --git a/src/JsonSchema/Constraints/Drafts/Draft2019/Draft2019Constraint.php b/src/JsonSchema/Constraints/Drafts/Draft2019/Draft2019Constraint.php
index 0b003b54..da459bb7 100644
--- a/src/JsonSchema/Constraints/Drafts/Draft2019/Draft2019Constraint.php
+++ b/src/JsonSchema/Constraints/Drafts/Draft2019/Draft2019Constraint.php
@@ -46,6 +46,7 @@ public function check(&$value, $schema = null, ?JsonPointer $path = null, $i = n
         $this->checkForKeyword('anyOf', $value, $schema, $path, $i);
         $this->checkForKeyword('oneOf', $value, $schema, $path, $i);
         $this->checkForKeyword('ifThenElse', $value, $schema, $path, $i);
+        $this->checkForKeyword('unevaluatedProperties', $value, $schema, $path, $i);
 
         $this->checkForKeyword('additionalProperties', $value, $schema, $path, $i);
         $this->checkForKeyword('items', $value, $schema, $path, $i);
diff --git a/src/JsonSchema/Constraints/Drafts/Draft2019/Factory.php b/src/JsonSchema/Constraints/Drafts/Draft2019/Factory.php
index cc490225..0c8e9f17 100644
--- a/src/JsonSchema/Constraints/Drafts/Draft2019/Factory.php
+++ b/src/JsonSchema/Constraints/Drafts/Draft2019/Factory.php
@@ -12,6 +12,7 @@ class Factory extends \JsonSchema\Constraints\Factory
     protected $constraintMap = [
         'schema' => Draft2019Constraint::class,
         'additionalProperties' => AdditionalPropertiesConstraint::class,
+        'unevaluatedProperties' => UnevaluatedPropertiesConstraint::class,
         'additionalItems' => AdditionalItemsConstraint::class,
         'dependentSchemas' => DependentSchemasConstraint::class,
         'dependentRequired' => DependentRequiredConstraint::class,
diff --git a/src/JsonSchema/Constraints/Drafts/Draft2019/UnevaluatedPropertiesConstraint.php b/src/JsonSchema/Constraints/Drafts/Draft2019/UnevaluatedPropertiesConstraint.php
new file mode 100644
index 00000000..0d7d40fd
--- /dev/null
+++ b/src/JsonSchema/Constraints/Drafts/Draft2019/UnevaluatedPropertiesConstraint.php
@@ -0,0 +1,112 @@
+<?php
+
+declare(strict_types=1);
+
+namespace JsonSchema\Constraints\Drafts\Draft2019;
+
+use JsonSchema\ConstraintError;
+use JsonSchema\Constraints\ConstraintInterface;
+use JsonSchema\Entity\ErrorBagProxy;
+use JsonSchema\Entity\JsonPointer;
+
+/**
+ * Proof-of-concept support for unevaluatedProperties.
+ *
+ * The current validator does not carry annotations between applicators, so this
+ * first implementation derives the evaluated property names from properties,
+ * patternProperties, and allOf branches in the current schema.
+ */
+class UnevaluatedPropertiesConstraint implements ConstraintInterface
+{
+    use ErrorBagProxy;
+
+    /** @var Factory */
+    private $factory;
+
+    public function __construct(?Factory $factory = null)
+    {
+        $this->factory = $factory ?: new Factory();
+        $this->initialiseErrorBag($this->factory);
+    }
+
+    public function check(&$value, $schema = null, ?JsonPointer $path = null, $i = null): void
+    {
+        if (!is_object($schema) || !property_exists($schema, 'unevaluatedProperties') || !is_object($value)) {
+            return;
+        }
+
+        if ($schema->unevaluatedProperties === true) {
+            return;
+        }
+
+        $evaluated = $this->collectEvaluatedProperties($schema, $value);
+        $unevaluated = array_diff_key(get_object_vars($value), array_flip($evaluated));
+        if (!$unevaluated) {
+            return;
+        }
+
+        $basePath = $path ?? new JsonPointer('');
+        foreach ($unevaluated as $propertyName => $propertyValue) {
+            $propertyPath = $basePath->withPropertyPaths(array_merge($basePath->getPropertyPaths(), [$propertyName]));
+
+            if (is_object($schema->unevaluatedProperties)) {
+                $propertyConstraint = $this->factory->createInstanceFor('schema');
+                $propertyConstraint->check($propertyValue, $schema->unevaluatedProperties, $propertyPath, $i);
+                if ($propertyConstraint->isValid()) {
+                    continue;
+                }
+
+                $this->addErrors($propertyConstraint->getErrors());
+                continue;
+            }
+
+            $this->addError(ConstraintError::UNEVALUATED_PROPERTIES(), $propertyPath, ['found' => $propertyName]);
+        }
+    }
+
+    /**
+     * @param object $schema
+     * @param object $value
+     *
+     * @return array<int, string>
+     */
+    private function collectEvaluatedProperties($schema, object $value): array
+    {
+        if (!is_object($schema)) {
+            return [];
+        }
+
+        $evaluated = [];
+
+        if (isset($schema->properties) && is_object($schema->properties)) {
+            $evaluated = array_merge($evaluated, array_keys(get_object_vars($schema->properties)));
+        }
+
+        if (isset($schema->patternProperties) && is_object($schema->patternProperties)) {
+            foreach (get_object_vars($value) as $propertyName => $_) {
+                foreach (array_keys(get_object_vars($schema->patternProperties)) as $pattern) {
+                    if (preg_match($this->createPregMatchPattern($pattern), (string) $propertyName)) {
+                        $evaluated[] = $propertyName;
+                        break;
+                    }
+                }
+            }
+        }
+
+        if (isset($schema->allOf) && is_array($schema->allOf)) {
+            foreach ($schema->allOf as $branch) {
+                $evaluated = array_merge($evaluated, $this->collectEvaluatedProperties($branch, $value));
+            }
+        }
+
+        return array_values(array_unique($evaluated));
+    }
+
+    private function createPregMatchPattern(string $pattern): string
+    {
+        $pattern = str_replace('\\p{digit}', '\\p{Nd}', $pattern);
+        $pattern = str_replace('\\p{Letter}', '\\p{L}', $pattern);
+
+        return '/' . str_replace('/', '\\/', $pattern) . '/u';
+    }
+}
diff --git a/tests/Constraints/UnevaluatedPropertiesTest.php b/tests/Constraints/UnevaluatedPropertiesTest.php
new file mode 100644
index 00000000..d8929aeb
--- /dev/null
+++ b/tests/Constraints/UnevaluatedPropertiesTest.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace JsonSchema\Tests\Constraints;
+
+use JsonSchema\DraftIdentifiers;
+use JsonSchema\Constraints\Constraint;
+
+class UnevaluatedPropertiesTest extends BaseTestCase
+{
+    protected $schemaSpec = DraftIdentifiers::DRAFT_2019_09;
+
+    public function getInvalidTests(): \Generator
+    {
+        yield [
+            '{"hello":"world","world":"hello","unexpected":true}',
+            '{
+                "$schema":"' . DraftIdentifiers::DRAFT_2019_09 . '",
+                "type":"object",
+                "unevaluatedProperties":false,
+                "allOf":[
+                    {"properties":{"hello":{"type":"string"}},"required":["hello"]},
+                    {"properties":{"world":{"type":"string"}},"required":["world"]}
+                ]
+            }',
+            Constraint::CHECK_MODE_STRICT,
+        ];
+    }
+
+    public function getValidTests(): \Generator
+    {
+        yield [
+            '{"hello":"world","world":"hello"}',
+            '{
+                "$schema":"' . DraftIdentifiers::DRAFT_2019_09 . '",
+                "type":"object",
+                "unevaluatedProperties":false,
+                "allOf":[
+                    {"properties":{"hello":{"type":"string"}},"required":["hello"]},
+                    {"properties":{"world":{"type":"string"}},"required":["world"]}
+                ]
+            }',
+            Constraint::CHECK_MODE_STRICT,
+        ];
+    }
+}