There is more than one artist with this name:
1) Delerium is from Vancouver, British Columbia, Canada, formed in 1987, originally as another side project (Intermix being the more techno-sounding project) of the influential industrial music act, Front Line Assembly.
Delerium has traditionally been a two-person project, but the only constant member throughout its history has been Bill Leeb. After Michael Balch left both Front Line Assembly and Delerium, Bill Leeb worked with Rhys Fulber, and the two released several albums under the Delerium moniker; these years saw a gradual stylistic change from darker ambient to a more danceable sound. A collaboration with Sarah McLachlan in their Karma album, "Silence", won them a certain amount of popular recognition and spawned a great deal of remixes.
After the release of Karma, Rhys Fulber left to pursue other interests, and Bill Leeb teamed up with producer Chris Peterson to release Poem. 2003, however, saw the reunion of Leeb and Fulber for the release of Chimera. The collaboration continued with Delerium’s most recent album, Nuages Du Monde. Delerium's music has additionally been featured in movies such as Lara Croft: Tomb Raider and Brokedown Palace.
2) Delerium was also a grunge act from Ottumwa, Iowa, USA. Formed by John Huston of Citrus Boyin 1994, Delerium played and recorded mostly in the Eastern Iowa area. It also included Paige Clause on drums and Sam Long on guitars. Delerium broke up shortly after 1994's album Pirate Alley, John and Sam went on to form punk rock band The Smirnoffs with Mark Langgin.
3) Often confused with Dj Delerium, a hardcore producer from the United States.