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.

Wonder Boy in Monster World, known in Japan as Wonder Boy V: Monster World III, is a side-scrolling action RPG originally developed by Westone Bit Entertainment and published by Sega for the Mega Drive/Genesis in 1991. It is the fifth game in the Wonder Boy series and the third game in the Monster World sub-series, following Wonder Boy in Monster Land (Super Wonder Boy: Monster World on the Japanese Sega Mark III) and Wonder Boy III: The Dragon's Trap (Monster World II: Dragon no Wana on the Japanese Game Gear). It was also the last Wonder Boy game that was given an official English release, until the Wii Virtual Console release of Monster World IV in 2012.