Cluster is a German experimental musical group who influenced the development of contemporary popular electronic and ambient music. They have recorded albums in a wide variety of styles ranging from experimental music to progressive rock, all of which had an avant-garde edge. Cluster has been active since 1971, releasing a total of 13 albums. Musician, writer and rock historian Julian Cope places three Cluster albums in his Krautrock Top 50 and "The Wire" places Cluster's self-titled debut album in their "One Hundred Records That Set The World On Fire". After a decade long hiatus Cluster reunited in April, 2007. They were selected to perform on June 15, 2007 at the opening of documenta 12, a major exhibition of modern and contemporary art held every five years in Kassel, Germany. In late 2007 Cluster continued to perform at concerts across Europe.