"Treehouse of Horror XI" is the first episode of the twelfth season of the American animated television series The Simpsons, the 249th episode overall, and the eleventh Halloween episode. The episode features "G-G-Ghost D-D-Dad", "Scary Tales Can Come True" and "Night of the Dolphin" and was written by Rob LaZebnik, John Frink and Don Payne and Carolyn Omine and directed by Matthew Nastuk.

The twelfth season of the American animated television series The Simpsons originally aired between November 2000 and May 2001. It began on Wednesday, November 1, 2000 with "Treehouse of Horror XI". The season contains four hold-over episodes from the season 11 (BABF) production line. The showrunner for the twelfth production season was Mike Scully. The season won and was nominated for numerous awards including two Primetime Emmy Awards wins and an Annie Award. Season 12 was released on DVD in Region 1 on August 18, 2009, Region 2 on September 28, 2009, and Region 4 on September 2, 2009.