The Elf on the Shelf is a popular Christmas tradition where families adopt a special elf who is said to watch over the children and report their behavior to Santa. The elf is often found in a hidden place in the home each morning, and the children can interact with him or her during the day. At night, the elf reports back to Santa on the children's behavior and brings back a new surprise the next morning. The Elf on the Shelf can be found at many retailers during the holiday season or purchased online.