The Scratch Orchestra, formed in London in 1969 by Cornelius Cardew, Michael Parsons and Howard Skempton, included visual and performance artists as well as musicians and other participants from diverse backgrounds, many of them without formal training. This article deals primarily with the earlier phase of the orchestra's activity, between 1969 and 1971. It describes the influence of the work of John Cage and Fluxus artists, involving the dissolution of boundaries between sonic and visual elements in performance and the use of everyday materials and activities as artistic resources. It assesses the conflicting impulses of discipline and spontaneity in the work of the Scratch Orchestra and in the parallel activity of the Portsmouth Sinfonia and other related groups. The emergence in the early 1970s of more controlled forms of compositional activity, in reaction against anarchic and libertarian aspects of the Scratch Orchestra's ethos, is also discussed.