Elf on a Shelf is a popular Christmas tradition that originated in the United States. The tradition involves placing an elf figure in various locations around the home throughout the holiday season to monitor the behavior of children. The elf is usually placed high up, out of reach, where children cannot easily move it. The idea is that the elf will report back to Santa if the children have been naughty or nice. The tradition has gained popularity in recent years, and many families now participate in it. It's usually around mid-November that families put out their Elf on a Shelf.