Wonder Boy III: Monster Lair (ワンダーボーイIII モンスター・レアー Wandā Bōi Surī: Monsutā Reā?, lit. "Wonder Boy III Monster Lair") is a side-scrolling action game developed by Westone Bit Entertainment that was originally released for the arcades by Sega in 1988. It is the third game in the Wonder Boy series and the last one released for the arcade. A console adaption was made by Hudson Soft, released in 1989 in Japan for the PC Engine CD and the subsequent North American release on the TurboGrafx-CD dropped the 'Wonder Boy III' title. It was also converted and released by Sega for the Mega Drive in Japan in 1990 and Europe in 1991.
