Born out of the hip-hop that came to England from the United States in the early ‘80s, trip-hop is a hybrid of the English hip-hop and techno that rule the club scene in the U.K. Although it has heavy beats and prevalent bass lines, trip-hop is more stripped down and airy. Because of the atmospheric sounds that are produced, trip-hop is fairly easy to recognize.

Combining almost every type of music from hip-hop and soul to Jamaican dub and jazz, trip-hop artists can pull samples from anywhere. Being mostly ambient, with slow but heavy beats, trip-hop sounds like lounge or mood music, but it is much more than that.

Most trip-hop acts come from the same place. Just as grunge emerged from Seattle in the early ‘90s, trip-hop has risen from the small town of Bristol, England. Because of this, many of the most important names in trip-hop have worked together in some way or another -- a sort of "six degrees of Bristol," you could say.

The roots for this genre go back to the early ‘80s and the rap/DJ collective known as the Wild Bunch. When the Wild Bunch broke up, members "Mushroom" Vowles and "Daddy G" Marshall teamed up with a local graffiti artist named 3D, and the fathers of trip-hop were formed: Massive Attack.

In 1991, the group released its groundbreaking debut, Blue Lines. Although the album was not a commercial success, it received critical acclaim and is now considered the trip-hop guide, doing for trip-hop what Dr. Dre's The Chronic did for today's rap.

One person featured on Blue Lines was a former member of the Wild Bunch known as Tricky Kid. Although not officially a member of Massive Attack, Tricky Kid did appear on Blue Lines and the group's second album, Protection. In 1995 he released a solo album and, perhaps sensing a newly found maturity, shortened his name to Tricky.

Maxinquaye, Tricky's solo debut, featured a sultry singer by the name of Martina Topley Bird. Bird's velvety voice was the antithesis of Tricky's raspy raps. Staying true to the genre's hip-hop lineage, Tricky and Bird covered classic raps like Public Enemy's "Black Steel in the Hour of Chaos" (shortened to "Black Steel" on Maxinquaye), Eric B. and Rakim's "Lyrics of Fury" (Pre-Millennium Tension) and Slick Rick's "Children's Story" (Nearly God). The most interesting thing about these covers, however, is that they're done by Bird, proving Lauryn Hill isn't the only woman who can rap and sing with equal talent.

But perhaps the best-known trip-hop act is yet another Bristol group known as Portishead. Geoff Barrow, the group's DJ/arranger, had worked with Massive Attack earlier in his career as well as Tricky -- if anyone knew the inner workings of trip-hop, it was Barrow. After spending much of his time as a remix producer, Barrow teamed up with singer Beth Gibbons and formed Portishead. In 1994 the group released Dummy, the soundtrack for a film they made called "To Kill a Dead Man." The album's first single, "Sour Times," was a surprise hit. Gibbons' melodic voice combined with choruses like "nobody loves me, it's true" made Morrissey seem almost happy. After some time off, the group finally re-emerged in 1997 with a self-titled album and last year released PNYC, a live album.

While Massive Attack continually talk about breaking up, Tricky and Portishead continue to release albums as newcomers are biting at their heels. Morcheeba and Mono have kept this genre moving and DJs are getting into the trip-hop groove, with DJ Shadow leading the way.

Now it seems like everyone has jumped on the bandwagon, whether they recognize it or not. Madonna introduced her listeners to trip-hop with her single "Frozen," as did the Sneaker Pimps with their song "6 Underground," which was mixed by another Wild Bunch alumnus, Nellee Hooper.