New Super Mario Bros. Wii is a 2D side-scrolling platform video game developed by Nintendo for the Wii. A follow-up to the 2006 Nintendo DS game New Super Mario Bros., it was first released in Australia, North America, and Europe in November 2009, followed by Japan a month later. Like other side-scrolling Super Mario games, the player controls Mario as he travels eight worlds and fights Bowser's henchmen to rescue Princess Peach. Up to four people can play in cooperative and competitive multiplayer modes, taking control of Mario as well as Luigi and one of two multicolored Toads. The game also introduces "Super Guide", which allows the player to watch a computer-controlled character complete a level.

The game was announced following a slight drop in profits, with Nintendo hoping its release would help to rejuvenate sales of the Wii. New Super Mario Bros. Wii was both critically and commercially successful, receiving particular praise for its multiplayer aspect, although some critics were disappointed by the lack of innovation compared to previous Super Mario titles. It received several honors, including the Best Wii Game award from the 2009 Spike Video Game Awards, IGN, and GameTrailers, and is the fourth best-selling game for the Wii as of March 2020, having sold 30.30 million copies worldwide.