WonderSwan (ワンダースワン, Wandāsuwan^?) was a line of handheld game consoles produced in Japan by Bandai between 1999 and 2003. It was developed by the late Gunpei Yokoi's company Koto and Bandai. The WonderSwan was made to compete with the Neo Geo Pocket Color and the market leader Nintendo's Game Boy Color (even though the developer for the WonderSwan, Gunpei Yokoi, developed the original Nintendo Game Boy).

The original WonderSwan was later replaced by the WonderSwan Color; although some WonderSwan Color games are compatible with the original WonderSwan, many are designed exclusively for the WonderSwan Color and show a message such as "This cartridge is for WonderSwan Color only" when run on the original WonderSwan.

The WonderSwan are playable both vertically and horizontally, and feature a fairly large library of games, including numerous first-party titles based on licensed anime properties, with significant third-party support from Square and Capcom. As it was a console designed essentially for the Japanese market, most of the games are in Japanese, with only a few featuring English text.

Gunpei Yokoi (横井 軍平, Yokoi Gunpei^?, September 10, 1941 – October 4, 1997), sometimes spelt Gumpei Yokoi, was a Japanese video game designer. He was a long-time Nintendo employee, creator of the Game Boy and Game & Watch handheld systems, and producer of several long-running and critically acclaimed video game franchises. In 1997, he was killed after being struck by a car on the Hokuriku Expressway.

Gunpei Yokoi was born in 1941 and grew up in Kyoto. He graduated from Doshisha University with a degree in electronics. He was first hired by Nintendo in 1965 to maintain the assembly-line machines used to manufacture its Hanafuda cards.