This essay analyses the Marxist features in the 1930s novels The Grapes of Wrath and Of Mice and Men by American writer John Steinbeck. Both novels tell the story of the hardship that migrant farm workers in California faced during the Depression. The assertion that Marxism was an influence on Steinbeck's writing is supported by comparisons of the two novels with The Manifesto of the Communist Party, written by Karl Marx and Frederick Engels in 1848. Key Marxist features, such as class conflict, alienation, workers' unionizing and proletarian revolution, are analysed and discussed via examples and quotations from the three texts. The concepts of Marxist literary theory, and Marxist features in Steinbeck's style, are also introduced. The conclusion is that, despite the author's own denial, Of Mice and Men and The Grapes of Wrath are Marxist in orientaion.