Acid house (also simply known as just "acid") is a subgenre of house music developed around the mid-1980s by DJs from Chicago. The style is defined primarily by the squelching sounds and basslines of the Roland TB-303 electronic bass synthesizer-sequencer, an innovation attributed to Chicago artists Phuture and Sleezy D circa 1986.

Acid house soon became popular in the United Kingdom and continental Europe, where it was played by DJs in the acid house and later rave scenes. By the late 1980s, acid house had moved into the British mainstream, where it had some influence on pop and dance styles.

Acid house brought house music to a worldwide audience. The influence of acid house can be heard in later styles of dance music including trance, hardcore, jungle, big beat, techno and trip hop.

Acid house's minimalist sound combined house music's ubiquitous programmed four-on-the-floor 4/4 beat with the electronic squelch sound produced by the Roland TB-303 electronic synthesizer-sequencer. The sound is commonly produced by raising the filter resonance and lowering the cutoff frequency of the synthesizer, along with programming the 303's accent, slide, and octave parameters, to create variation in otherwise simple bass patterns. "Exploration of texture" is preferred over melody; "a refusal of the metaphysical priorities of western music discourse". Other elements, such as synthetic strings and stabs, were usually minimal. Sometimes tracks were instrumentals, such as Phuture's "Acid Tracks", or contained full vocal performances, such as DJ Pierre's Pfantasy Club's "Fantasy Girl", while others were essentially instrumentals complemented by the odd spoken word "drop-in", such as Phuture's "Slam".

There are conflicting accounts about the origin of the term acid. One self-claimed account by members of Phuture points to their own "Acid Tracks". Before the song was given a title for commercial release, it was played by DJ Ron Hardy at a nightclub where psychedelic drugs were reportedly used. The club's patrons called the song "Ron Hardy's Acid Track" (or "Ron Hardy's Acid Trax"). The song was released with the title "Acid Tracks" on Larry Sherman's label Trax Records in 1987. Sources differ on whether it was Phuture or Sherman who chose the title; Phuture's DJ Pierre says the group did because the song was already known by that title, but DJ Pierre says he chose the title because the song reminded him of acid rock. Regardless, after the release of Phuture's song, the term acid house came into common parlance. Another claim is that Psychic TV's frontperson Genesis Breyer P-Orridge actually named the genre.

Some accounts say the reference to "acid" may be a celebratory reference to psychedelic drugs in general, such as LSD, as well as the popular club drug Ecstasy (MDMA). According to Professor Hillegonda Rietveld, a researcher specializing in electronic dance music, it was the house sensibility of Chicago, in a club like Hardy's The Music Box, that afforded it its initial meaning. In her view "acid connotes the fragmentation of experience and dislocation of meaning due to the unstructuring effects on thought patterns which the psychedelic drug LSD or 'Acid' can bring about". In the context of the creation of "Acid Tracks" it indicated a concept rather than the use of psychedelic drugs in itself.

Some accounts disavow psychedelic connotations. One theory, holding that acid was a derogatory reference towards the use of samples in acid house music, was repeated in the press and in the British House of Commons. In this theory, the term acid came from the slang term "acid burning", which the Oxford Dictionary of New Words calls "a term for stealing". In 1991, UK Libertarian advocate Paul Staines claimed that he had coined this theory to discourage the government from adopting anti-rave party legislation.

The name of acid jazz is derived from that of acid house, which served as one of the inspirations for the genre's development.