An "elf on the shelf" is a fun Christmas tradition where an elf doll is placed in different locations around your home to keep an eye on children's behavior leading up to Christmas. Each morning, children will look for the elf's new location and guess what mischief he got up to during the night. It's a playful way to keep children excited about the holiday season and encourage good behavior. To get started, find a special elf doll, place it in a prominent spot, and come up with some fun activities for it to do each day.