The article discusses the origins and popularity of hip-hop music and the challenges faced by libraries in establishing and maintaining a hip-hop collection. Strictly defined, hip-hop refers to the entire cultural constellation that accompanies rap music, which in 2001 surpassed country music as the most popular musical genre in the United States. Establishing and maintaining a hip-hop collection that pleases patrons and credibly covers a rapidly evolving field is tricky. Because of hip-hop's mass appeal, public libraries definitely need guidance. Rap falls into six primary categories: "gangsta," which focuses on murder, money, and mayhem; apolitical pop, which features a danceable beat and easygoing lyrics; political, whose calling card is socially analytical lyrics; positive, which encourages listeners to become more aware of social and personal ills and to take steps to change them; experimental, which continually modifies its style; and, finally, feminist, which challenges the implicit definition of rap as music created by and for males. To separate the wheat from the whack, librarians can consult sterling references like All Music Guide to Hip-Hop and Rough Guide to Hip-Hop, as well as the timely and competent reviews in Rolling Stone.