Underworld are a British electronic music group formed in 1987 in Cardiff, Wales, and the principal collaborative project of Karl Hyde and Rick Smith.

After briefly performing as a funk and synth-pop outfit, resulting in two albums between 1988 and 1989, Underworld gained prominence after pivoting to dance and techno, releasing albums including Dubnobasswithmyheadman (1994), Second Toughest in the Infants (1996) and Beaucoup Fish (1999), as well as singles "Born Slippy Nuxx" and "Dark & Long (Dark Train)".

Known for their atmospheric, progressive compositions, Hyde's cryptic and stream of consciousness lyrics, and dynamic live performances, Underworld have influenced a wide range of artists, and have featured in soundtracks and scores for films and television.

In the late 1970s, Karl Hyde and Rick Smith formed a band in Cardiff called the Screen Gemz, which was influenced by Kraftwerk and reggae. They were joined by bassist Alfie Thomas, drummer Bryn Burrows, and keyboardist John Warwicker in forming Freur. The band signed to CBS Records and released Doot-Doot (1983). Freur disbanded in 1986 after CBS withheld the UK release of their follow-up album, Get Us out of Here.

In 1987, Hyde, Smith, Thomas, Burrows and bassist Baz Allen formed Underworld, named after the 1985 horror film Underworld, which was scored by Freur. Underworld signed to Sire Records and released the album Underneath the Radar in 1988. Following the departure of Burrows, they released another album, Change the Weather, in 1989.

This lineup, referred to by the group as "Underworld Mk1", disbanded in 1990. The band had just finished a stadium tour opening for Eurythmics and had incurred a large debt that Smith spent a year attempting to pay off. Hyde stayed in Los Angeles while Smith returned to the United Kingdom. Hyde recalled feeling miserable during the Eurythmics tour, and said of Underworld Mk1, "We’d subvert what we naturally did to fit an idea of what was going to be successful in the charts, and we just weren’t very good at it. We realised we were a band trapped in the body of another band. We were denying what we were."

After a break—to concentrate on, among other things, art/design project Tomato—Hyde and Smith relocated from South Wales to Romford, Greater London, in 1992. At this time they recruited DJ Darren Emerson and signed to Steven Hall's Junior Boys Own label. After several releases and remixes as Lemon Interupt and Steppin' Razor, they readopted the Underworld moniker. They produced danceable techno as a trio ("Underworld Mk2").

The addition of Emerson completed Underworld's techno/rock fusion and seemed to eliminate the pop elements in the original duo's work. Their first album, Dubnobasswithmyheadman, was considered more accessible than the group's earlier material and crossed a large spectrum of dance music. The signature Hyde lyrics were in place: poetic, hypnotic and whispered; mixing conventional song writing with the use of found material from overheard conversations, answering machine recordings and the like. Hyde had been the lead singer in Underworld Mk1 but the original Hyde/Smith dance material was lyric-free as was most of the electronic music emerging from the aftermath of acid house.