Judith Lewis, better known by her pen name Cassandra Clare, is an American author of young adult fiction, best known for her bestselling series The Mortal Instruments.

Young adult literature (YA) is typically written for readers aged 12 to 18, and includes most of the themes found in adult fiction, such friendship, substance abuse, alcoholism, and sexuality. Stories that focus on the challenges of youth may be further categorized as social or coming-of-age novels.