During the 1930s San Francisco's most ambitious public murals were painted by artists on the left. In this study, Anthony Lee shows how these painters, led by Diego Rivera, sought to transform murals into a vehicle for their rejection of the economic and political status quo and their support of labor and radical ideologies, including Communism. In addressing these subjects, the mural painters developed a new imagery, based on the activities of the city's laboring population - its efforts to organize, its protests, its strikes. Painting on the Left relates the development of wall painting to the city's international expositions of 1915 and 1939, the new museums and art schools, corporate patrons and government administrators, and the concerns of immigrants and ethnic groups. It examines how murals became, and the extent to which they remained, "public," and it looks at how mural painters struggled against developments in art and politics that threatened their practice: the growing acceptance of modernist easel painting, the vagaries of New Deal patronage, and a wartime nationalism hostile to radical politics.