Elf on the Shelf is a popular Christmas tradition where an elf doll is placed in a home to keep an eye on children's behavior and report back to Santa. The elf, which is traditionally placed somewhere different each day, has its own set of rules to follow. These rules include not moving when children are watching, not being touched, and not speaking. The elf is usually named, and children can communicate with it through writing notes or whispering. The elf's main purpose is to create excitement and magic around Christmas, and it is a fun and interactive way to encourage good behavior in children.