Elf on the Shelf is a popular Christmas tradition that typically involves placing a small elf doll or figurine in a family home to keep an eye on children's behavior and report back to Santa. The tradition is believed to have originated in Germany, and it gained widespread popularity in the United States around the 1990s. Today, Elf on the Shelf is commonly observed from the day after Thanksgiving until Christmas Eve, though some families may choose to keep their elf out longer.