During the mid-1960s, sculptors in the United States and Europe simultaneously lost interest in making objects. Instead, under banners such as "Anti-Form" and "Arte Povera", they began to present undifferentiated matter as sculpture: industrial felt, lead, dirt, vegetables, even live animals. Such heaps, arrays, and environments seemed to mark the end of modern sculpture. They dominated sculptural debate at the time of their appearance, and they have since proved enormously influential on contemporary art. This is the first book to treat such work as a separate topic.