The WonderSwan was a handheld game console released in Japan by Bandai. Developed in collaboration with Gunpei Yokoi's company Koto Laboratory, it was the final piece of hardware Yokoi worked on before his death in 1997. Launched in Japan in March 1999 during the sixth generation of video game consoles, the WonderSwan was followed by two upgraded models, the WonderSwan Color and SwanCrystal, before Bandai discontinued the line in 2003. Throughout its lifespan, no version of the WonderSwan was officially released outside Japan.

Powered by a 16-bit processor, the WonderSwan was designed as both a more powerful and affordable alternative to its 8-bit competitors, Nintendo's Game Boy Color and SNK's Neo Geo Pocket Color, while offering notably long battery life from a single AA battery. Later iterations improved the handheld’s display, introducing color for enhanced visual quality. One of its distinguishing features was its dual-orientation design, allowing gameplay in both vertical and horizontal modes. The WonderSwan also cultivated a unique library, featuring numerous first-party titles based on licensed anime properties and strong third-party support from developers such as Squaresoft, Namco, Capcom and Banpresto.

In total, all variations of the WonderSwan combined to sell an estimated 3.5 million units, capturing up to 8% of the Japanese handheld gaming market at its peak before being overshadowed by Nintendo's Game Boy Advance. In retrospect, despite its limited commercial success, the WonderSwan is often praised for its innovation and potential, as well as its brief yet noteworthy challenge to Nintendo's dominance in the handheld gaming space.

Founded in 1950 by Naoharu Yamashina, Bandai was originally a manufacturer of toy cars and plastic models, but became a major player in the toy industry through the licensing of popular anime characters beginning with Tetsuwan Atomu in 1963. In the 1970s, Bandai manufactured both LCD games based on television programs and dedicated consoles. In 1982, the company released the Intellivision in Japan, and in 1985 it became one of the first third-party licensees on the Family Computer. However, the company's greatest success in electronic games, was the Tamagotchi virtual pet first released in 1996. Despite plans for Bandai to merge with Sega to form Sega Bandai Ltd. in 1997, the merger was called off suddenly. Bandai's board of directors decided to oppose the merger less than a week after approving it, and Sega in turn decided to accept Bandai's actions at an emergency board meeting later that day. Bandai president Makoto Yamashina took responsibility for failing to gain the support of his company for the merger. As a result, Bandai entered the market without outside support.

Engineer Gunpei Yokoi is known for creating the Game Boy handheld system at Nintendo. After the failure of the Virtual Boy, however, he left the company in 1996 in order to create his own engineering firm, Koto Laboratory. It was then that Bandai approached Yokoi to create the WonderSwan to compete with the Game Boy. Yokoi was involved in development of the new handheld, but died in 1997 in a car accident before it was released.

The WonderSwan was officially unveiled in Tokyo on October 8, 1998. Bandai chose the name of the system to highlight its aesthetics and technical capabilities because the swan is recognized as an elegant bird with powerful legs that aid its graceful swimming. The company promised a 30-hour battery life, a low retail price, and a launch lineup of roughly fifty games.

The WonderSwan launched on March 4, 1999 and was available in nine casing colors: pearl white, skeleton green, silver metallic, skeleton pink, blue metallic, skeleton blue, skeleton black, camouflage, and gold. Three limited edition two-tone models were also released in frozen mint, sherbet melon and soda blue. These colors were chosen through an online poll at Bandai’s website, with the metallic and pearl white models being discontinued on July 22 to make room for the special two-tone editions. Despite Nintendo's release of the Game Boy Color five months before, Bandai remained confident that the WonderSwan and its monochromatic FSTN display would perform well because the original black-and-white Game Boy had previously been more successful than its color-screen competitors, the Game Gear and Atari Lynx, on the basis of its battery life and the quality of its game library. With a retail price ¥4,800, the WonderSwan was also cheaper than its competition. In 2000, Bandai signed an agreement with Mattel to bring the handheld to North America, but ultimately decided against a Western release. The exact reason for this is unknown, but the crowded handheld video game console market has been suggested as a factor.

Later that year, Bandai announced the WonderSwan Color which would incorporate a passive matrix FSTN color screen while retaining backward compatibility with the original WonderSwan. It was released on December 9 in Japan and was available in pearl blue, pearl pink, crystal black, crystal blue, and crystal orange. The launch was a moderate success, with the system selling 270,632 units in under a month after its release. Before the WonderSwan Color could be released, however, Nintendo announced the Game Boy Advance, which featured superior hardware. The WonderSwan Color still retailed at a lower price point at ¥6,800 compared to the Advance at ¥9,800, but despite peaking at 8% of the handheld market share in Japan, the WonderSwan's sales never recovered after the Game Boy Advance reached store shelves in March 2001.