Clement Greenberg (January 16, 1909 - May 7, 1994) was an influential American art critic who was closely associated with the institutionalization of abstract art in the United States. In particular he promoted the Abstract Expressionist movement led by Jackson Pollock.

Greenberg made his name as an art critic with his essay Avant Garde and Kitsch, published in 1939. In this article Greenberg claimed that avant-garde and Modernist art was a means to resist the 'dumbing down' of culture caused by consumerism. Greenberg termed this 'kitsch', a word that his essay popularised, though its connotations have since changed. Modern art, like philosophy, explored the conditions under which we experience and understand the world. It does not simply provide information about it — in the manner of an illustratively accurate depiction of the world. "Avant Garde and Kitsch" was also a politically motivated essay in part a response to the destruction and repression of Modernist Art in Nazi Germany and the Soviet Union and its replacement with state ordained styles of "Aryan" art and 'Socialist Realism'.

Greenberg believed Modernism provided a critical commentary on experience. It was constantly changing to adapt to kitsch culture, which was itself always developing. In the years after World War Two, Greenberg came to believe that the best avant-garde artists were emerging in America rather than Europe. In the 1955 essay "American Type Painting" he promoted the work of Pollock, Willem De Kooning, Hans Hofmann and the other Abstract Expressionists as next stage in Modernist art, arguing that Modernist art was moving towards greater emphasis on the 'flatness' of the picture plane. Greenberg's view that after the war the United States had become the guardian of 'advanced art' was taken up in some quarters as a reason for using Abstract Expressionism as the basis for Cultural Propaganda exercises.

These views led Greenberg to reject Pop Art in the 1960s, which was influenced by kitsch culture. Through the 1960s and 1970s Greenberg remained an influential figure on a younger generation of critics including Michael Fried and Rosalind Krauss . Greenberg's antagonism to 'Postmodernist' theories and socially engaged movements in art caused a backlash amongst both artists and art historians which came to be known as "Clembashing".