Steampunk is a sub-genre of science fiction that typically features steam-powered machinery, especially in a setting inspired by industrialised Western civilisation during the 19th century. Steampunk works are often set in an alternative history of the 19th century's British Victorian era or American "Wild West", in a post-apocalyptic future during which steam power has regained mainstream use, or in a fantasy world that similarly employs steam power. Steampunk perhaps most recognisably features anachronistic technologies or retro-futuristic inventions as people in the 19th century might have envisioned them, and is likewise rooted in the era's perspective on fashion, culture, architectural style, and art. Such technology may include fictional machines like those found in the works of H. G. Wells and Jules Verne, or the modern authors Philip Pullman, Scott Westerfeld, Stephen Hunt and China Miéville. Other examples of steampunk contain alternative history-style presentations of such technology as lighter-than-air airships, analog computers, or such digital mechanical computers as Charles Babbage's Analytical Engine.

Steampunk may also, though not necessarily, incorporate additional elements from the genres of fantasy, horror, historical fiction, alternate history, or other branches of speculative fiction, making it often a hybrid genre. The term steampunk's first known appearance was in 1987, though it now retroactively refers to many works of fiction created even as far back as the 1950s or 1960s.

Steampunk also refers to any of the artistic styles, clothing fashions, or subcultures, that have developed from the aesthetics of steampunk fiction, Victorian-era fiction, art nouveau design, and films from the mid-20th century. Various modern utilitarian objects have been modded by individual artisans into a pseudo-Victorian mechanical "steampunk" style, and a number of visual and musical artists have been described as steampunk.