Advanced Dungeons & Dragons: Planescape RPG

Advanced Dungeons & Dragons: Planescape RPG is a 18-book series with 18 released primary works first released in 1991 with contributions by Monte Cook, Wolfgang Baur, Lester W. Smith, David Zeb Cook, Skip Williams, Rick Swan, Dori Jean Hein, Tim Beach, J.M. Salsbury, Richard Baker, Ken Rolston, Ray Vallese, Colin McComb, Dale Donovan, Ray Valllese, Bill Slavicsek, and Bruce R. Cordell.