Elf on the Shelf is a popular holiday toy and tradition that originated in the United States in the early 2000s. The concept involves a small elf doll that is placed on a shelf or other high spot in a home, where it becomes a playful and mischievous guardian who watches children's behavior during the holiday season. The toy is typically sold with a companion book that tells the story of the elf's history and its role in monitoring children's behavior. The tradition has grown in popularity over the years and is now widely celebrated by families around the world.