diff --git a/includes/activity/class-activity.php b/includes/activity/class-activity.php
index 8799238..3164993 100644
--- a/includes/activity/class-activity.php
+++ b/includes/activity/class-activity.php
@@ -68,7 +68,7 @@ class Activity extends Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-context
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -82,7 +82,7 @@ class Activity extends Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object-term
 	 *
 	 * @var string
-	 *    | Base_Objectr
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -97,7 +97,7 @@ class Activity extends Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-actor
 	 *
 	 * @var string
-	 *    | \ActivityPhp\Type\Extended\AbstractActor
+	 *    | Actor
 	 *    | array<Actor>
 	 *    | array<Link>
 	 *    | Link
@@ -116,8 +116,8 @@ class Activity extends Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-target
 	 *
 	 * @var string
-	 *    | ObjectType
-	 *    | array<ObjectType>
+	 *    | Base_Object
+	 *    | array<Base_Object>
 	 *    | Link
 	 *    | array<Link>
 	 */
@@ -132,7 +132,7 @@ class Activity extends Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-result
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -149,7 +149,7 @@ class Activity extends Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-origin
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -162,7 +162,7 @@ class Activity extends Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-instrument
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -176,7 +176,7 @@ class Activity extends Base_Object {
 	 *
 	 * @see https://www.w3.org/TR/activitypub/#object-without-create
 	 *
-	 * @param string|Base_Objectr|Link|null $object
+	 * @param string|Base_Object|Link|null $object
 	 *
 	 * @return void
 	 */
diff --git a/includes/activity/class-base-object.php b/includes/activity/class-base-object.php
index 3b6703b..7d81c2b 100644
--- a/includes/activity/class-base-object.php
+++ b/includes/activity/class-base-object.php
@@ -49,9 +49,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attachment
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -65,9 +65,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attributedto
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -80,9 +80,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-audience
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -115,7 +115,7 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-context
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -210,9 +210,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-inreplyto
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -225,9 +225,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-location
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -239,7 +239,7 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-preview
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -287,7 +287,7 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-summary
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
 	 *    | null
 	 */
@@ -313,9 +313,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tag
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -348,9 +348,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-to
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -363,9 +363,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-bto
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -378,9 +378,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-cc
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -393,9 +393,9 @@ class Base_Object {
 	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-bcc
 	 *
 	 * @var string
-	 *    | ObjectType
+	 *    | Base_Object
 	 *    | Link
-	 *    | array<ObjectType>
+	 *    | array<Base_Object>
 	 *    | array<Link>
 	 *    | null
 	 */
@@ -433,7 +433,7 @@ class Base_Object {
 	 *
 	 * @see https://www.w3.org/TR/activitypub/#source-property
 	 *
-	 * @var ObjectType
+	 * @var Base_Object
 	 */
 	protected $source;
 
diff --git a/includes/class-sanitizer.php b/includes/class-sanitizer.php
new file mode 100644
index 0000000..2deaaa2
--- /dev/null
+++ b/includes/class-sanitizer.php
@@ -0,0 +1,136 @@
+<?php
+
+namespace Activitypub;
+
+class Sanitizer {
+
+	/**
+	 * Sanitize a multi-dimensional array
+	 *
+	 * @param array $array The array to sanitize.
+	 *
+	 * @return array The sanitized array.
+	 */
+	public static function sanitize_array( $array ) {
+		$sanitized_array = array();
+
+		foreach ( $array as $key => $value ) {
+			$key = self::sanitize_key( $key );
+
+			if (
+				in_array(
+					$key,
+					array(
+						'summary_map',
+						'summaryMap',
+						'content_map',
+						'contentMap',
+					),
+					true
+				)
+			) {
+				$sanitized_array[ $key ] = self::sanitize_map( $value );
+			} elseif (
+				in_array(
+					$key,
+					array(
+						'inbox',
+						'outbox',
+						'followers',
+						'following',
+					),
+					true
+				)
+			) {
+				if ( is_string( $value ) ) {
+					$sanitized_array[ $key ] = sanitize_url( $value );
+				} else {
+					$sanitized_array[ $key ] = '';
+				}
+			} elseif ( in_array( $key, array( 'summary', 'content' ), true ) ) {
+				$sanitized_array[ $key ] = self::sanitize_html( $value );
+			} elseif ( is_array( $value ) ) {
+				$sanitized_array[ $key ] = self::sanitize_array( $value );
+			} else {
+				$sanitized_array[ $key ] = self::sanitize_value( $value );
+			}
+		}
+
+		return $sanitized_array;
+	}
+
+	/**
+	 * Sanitize a value.
+	 *
+	 * @param string $value The value to sanitize.
+	 *
+	 * @return string The sanitized value.
+	 */
+	public static function sanitize_value( $value ) {
+		if ( is_email( $value ) ) {
+			return sanitize_email( $value );
+		}
+
+		if ( filter_var( $value, FILTER_VALIDATE_URL ) ) {
+			return sanitize_url( $value );
+		}
+
+		return sanitize_text_field( $value );
+	}
+
+	/**
+	 * Sanitize HTML.
+	 *
+	 * @param string $value The value to sanitize.
+	 *
+	 * @return string The sanitized value.
+	 */
+	public static function sanitize_html( $value ) {
+		if ( is_array( $value ) ) {
+			return '';
+		}
+
+		global $allowedtags;
+		$tags = array_merge(
+			$allowedtags,
+			array( 'p' => array() )
+		);
+
+		$value = \preg_replace( '@<(script|style)[^>]*?>.*?</\\1>@si', '', $value );
+		$value = \strip_shortcodes( $value );
+		$value = \wptexturize( $value );
+		$value = \wp_kses( $value, $tags );
+
+		return $value;
+	}
+
+	/**
+	 * Sanitize a translation map
+	 *
+	 * @param array $map The map to sanitize.
+	 *
+	 * @return array The sanitized map.
+	 */
+	public static function sanitize_map( $map ) {
+		$sanitized_map = array();
+
+		foreach ( $map as $key => $value ) {
+			$key = self::sanitize_key( $key );
+
+			$sanitized_map[ $key ] = self::sanitize_html( $value );
+		}
+
+		return $sanitized_map;
+	}
+
+	/**
+	 * Sanitize an array key
+	 *
+	 * @param string $key The key to sanitize.
+	 *
+	 * @return string The sanitized key.
+	 */
+	public static function sanitize_key( $key ) {
+		return \preg_replace( '/[^a-zA-Z0-9_\-]/', '', $key );
+	}
+}
diff --git a/tests/test-class-activitypub-sanitizer.php b/tests/test-class-activitypub-sanitizer.php
new file mode 100644
index 0000000..6cfabaa
--- /dev/null
+++ b/tests/test-class-activitypub-sanitizer.php
@@ -0,0 +1,43 @@
+<?php
+class Test_Activitypub_Sanitizer extends WP_UnitTestCase {
+	/**
+	 * @dataProvider the_data_provider
+	 */
+	public function test_sanitize_array( $source, $target ) {
+		$sanitizer = new Activitypub\Sanitizer();
+		$this->assertEquals( $target, $sanitizer->sanitize_array( $source ) );
+	}
+
+	public function the_data_provider() {
+		return array(
+			array(
+				array(
+					'type"§$' => '<p>Create</p>',
+					'content' => '<p>Content</p><script>content</script>',
+					'contentMap' => array(
+						'en' => '<p>Content</p><script>content</script>',
+					),
+					'nameMap' => array(
+						'en' => '<div>Content</div><script>content</script>',
+					),
+					'inbox' => 'https://example.org/inbox',
+					'outbox' => 'example.org/outbox',
+					'name' => 'Gifts\'+OR+1=1--',
+				),
+				array(
+					'type' => 'Create',
+					'content' => '<p>Content</p>',
+					'contentMap' => array(
+						'en' => '<p>Content</p>',
+					),
+					'nameMap' => array(
+						'en' => 'Content',
+					),
+					'inbox' => 'https://example.org/inbox',
+					'outbox' => 'http://example.org/outbox',
+					'name' => 'Gifts\'+OR+1=1--',
+				),
+			),
+		);
+	}
+}