Wonder Boy in Monster World, known in Japan as Wonder Boy V: Monster World III, is a side-scrolling action role-playing game originally developed by Westone and published by Sega for the Mega Genesis in 1991.

Wonder Boy In Monster World puts you in control of Shion in his quest to save Monster World from the evil BioMeka. It controls like your standard platform game: run, jump, crouch, and kill enemies. The game is filled with Adventure elements such as talking to townsfolk, collecting money to buy items, extending your life bar by collecting hearts, and equipping a large variety of armor, weapons and magic.

Shion travels through the many interconnected regions of Monster World, all the while collecting increasingly powerful equipment in the form of many different swords, spears, shields, suits of armor, and boots.

The game introduced a one slot save feature to save progress at inns throughout the game world. In the original Japanese version Shion returned to the inn last saved at upon death (and was charged its fee accordingly), so returning to an inn in order to save is a simple matter of allowing Shion to be killed. In the English-language Mega Drive versions this was changed to a "Game Over" screen; this made it often tedious to return to the inns early in the game when Return magic hadn't been obtained yet.