The Elf on the Shelf is a popular Christmas tradition that originated in the United States. It involves placing an elf doll in a prominent location in the home and having it observe the family's behavior for the holiday season. The elf then reports its observations back to Santa Claus, who determines whether the children have been naughty or nice. The elf is typically hidden in a different location each night, so children will look for it and wonder what it has seen. It's a fun and interactive way to engage children in the spirit of Christmas.