The Girls Next Door (also known as The Girls of the Playboy Mansion) is a reality television series which focuses on the lives of Hugh Hefner's girlfriends who live with him at the Playboy Mansion. The series was created by executive producer Kevin Burns and Hefner, founder of Playboy magazine. The series premiered on the E! cable network on August 7, 2005 and ran for 6 seasons. The first five seasons centered around then-girlfriends, Holly Madison, Bridget Marquardt and Kendra Wilkinson. The sixth and final season premiered on October 11, 2009 and introduced Hefner's new girlfriends, Crystal Harris, who eventually went on to marry Hefner, and twins Kristina and Karissa Shannon.

The success of the series was followed by several spin-offs, including Kendra and Holly's World.