diff --git a/README.md b/README.md
index c822625..63eae75 100644
--- a/README.md
+++ b/README.md
@@ -102,8 +102,20 @@ Type|Description
 `Type::BOOLEAN`|Value must be a boolean or ([**considered bool for GET rules**](#boolean-coercion-from-string-for-search-parameters))
 `Type::ARRAY`|Value must be a JSON array
 `Type::OBJECT`|Value must be a JSON object
+`Type::ENUM`|Value must be exactly one of pre-defined values ([**more information**](#typeenum))
 `Type::NULL`|Value must be null or ([**considered null for GET rules**](#null-coercion-from-string-for-search-parameters))
 
+#### `Type::ENUM`
+
+Provided value for property must be an exact match of any value provided as an `array` to the second argument of `type(Type::ENUM, <whitelist>)`
+```php
+Rules->type(Type::ENUM, [
+  "FOO",
+  "BAR"
+]);
+```
+Any value that isn't `"FOO"` or `"BAR"` will be rejected.
+
 #### Boolean coercion from string for search parameters
 Search parameters are read as strings, a boolean is therefor coerced from the following rules.
 
diff --git a/src/Rules.php b/src/Rules.php
index a08ca59..c498ccb 100644
--- a/src/Rules.php
+++ b/src/Rules.php
@@ -10,12 +10,13 @@
 	enum Type {
 		use xEnum;
 		
+		case NULL;
+		case ENUM;
+		case ARRAY;
 		case NUMBER;
 		case STRING;
-		case BOOLEAN;
-		case ARRAY;
 		case OBJECT;
-		case NULL;
+		case BOOLEAN;
 	}
 
 	class Rules {
@@ -28,6 +29,8 @@
 		// Typed array of type ReflectRules\Type
 		public ?array $types = null;
 
+		public ?array $enum = null;
+
 		private bool $default_enabled = false;
 		public mixed $default;
 
@@ -72,8 +75,16 @@
 			return $this;
 		}
 
-		// Set property Types
-		public function type(Type $type): self {
+		// Add Type constraint with optional argument
+		public function type(Type $type, mixed $arg = null): self {
+			if ($type === Type::ENUM) {
+				if (!is_array($arg)) {
+					throw new \Exception("Expected type 'array' of ENUM values as second argument");
+				}
+
+				$this->enum = $arg;
+			}
+
 			$this->types[] = $type;
 			return $this;
 		}
@@ -121,6 +132,11 @@
 			return is_bool($value);
 		}
 
+		private function eval_type_enum(mixed $value): bool {
+			// Return true if value isn't boolean and exists in enum array
+			return !is_bool($value) && in_array($value, $this->enum);
+		}
+
 		/*
 			## Public eval methods
 			These are the entry-point eval methods that in turn can call other
@@ -152,6 +168,7 @@
 					Type::BOOLEAN => $match = $this->eval_type_boolean($value, $scope),
 					Type::ARRAY,
 					Type::OBJECT  => $match = is_array($value),
+					Type::ENUM    => $match = $this->eval_type_enum($value),
 					Type::NULL    => $match = is_null($value)
 				};
 
diff --git a/src/Ruleset.php b/src/Ruleset.php
index d9b9193..57f1a1e 100644
--- a/src/Ruleset.php
+++ b/src/Ruleset.php
@@ -84,6 +84,12 @@
 				// List names of each allowed type
 				$types = implode(" or ", array_map(fn($type): string => $type->name, $rules->types));
 
+				// List allowed enum values
+				if ($rules->enum) {
+					$values = implode(" or ", array_map(fn($value): string => "'{$value}'", $rules->enum));
+					$this->add_error($name, "Value must be exactly: {$values}");
+				}
+
 				$this->add_error($name, "Value must be of type {$types}");
 			}