Unlike traditional art works, installation art has no autonomous existence. It is usually created at the exhibition site, and its essence is spectator participation. Installation art originated as a radical art form presented only at alternative art spaces; its assimilation into mainstream museums and galleries is a relatively recent phenomenon. The move of installation art from the margin to the center of the art world has had far-reaching effects on the works created and on museum practice. This is the first book-length study of installation art.