The Grapes of Wrath is the stage play adaptation of the novel by the same name by Frank Galati. The critically-acclaimed novel version by John Steinbeck and the play by Galati have essentially the same themes. The first prominent theme of The Grapes of Wrath is the financial and social struggles that many Americans—mostly lower-class and middle-class citizens—faced during the Great Depression of the mid-20th century. The play paints a humane portrait of migrants from the Midwest and Great Plains who moved to the West Coast, particularly the agricultural regions of California. Steinbeck, who was a reporter for a San Francisco newspaper, based many of his characters on actual people he had interviewed as a journalist.

In this regard, The Grapes of Wrath could be considered a realist form of fiction, or one that heavily uses factual details to add dimensions to the narrative or characters. The other significant theme of Galati's play is the predatory nature of America's banking system, and the banks' callous treatment of working-class Americans, particularly poor farmers. Many of the Oklahoma-based tenant farmers who eventually became migrants, or economic refugees, seeking new opportunities in California had their farms foreclosed by banks.

The other theme of the story is the perseverance of the working-class American, especially during the era of economic depression. The daily life struggles and broader challenges caused by poverty are vividly depicted in The Grapes of Wrath, in the same way Dorothea Lange's documentary photo essays showed the general American public the severity of the Great Depression.

Another theme of the narrative is the concept of leadership. The protagonist, Tom Joad, is the youngest member of his family and yet he becomes the leader of the clan. In contrast, the Great Depression has broken several families and caused disorienting social chaos. Likewise, the U.S. government showed lack of leadership in handling the economic crisis, which allowed corporate America, particularly the banking system, to exploit the people.