Clement Greenberg was the most influential theorizer and promoter of Modernism in America during the middle years of the twentieth century. His advocacy helped to bring about the institutionalization of Abstract Expressionism and to secure the dominance of American Modernist art in the immediate post-war period. However, Greenberg’s subsequent rejection of Pop Art and Conceptualism led to a period in which his writings and his preferences were regularly condemned. These attacks arose from what was perceived as his dogmatic advocacy of abstraction, and his distaste for commercial popular culture – what he called ‘kitsch’ in one of his most famous essays, ‘Avant Garde and Kitsch’ (1939).