Lorraine Hansberry uses Langston Hughes' poem "Harlem" as an epigraph to her play "A Raisin in the Sun." An epigraph is when an author chooses to place a quote or poem, etc. by another author that serves to introduce a theme in the work. For instance, "Harlem" is filled with metaphors and similes about what happens to a dream deferred (at one point, the speaker asks if it dries up like a raisin in the sun). Hansberry, therefore, uses an allusion to Hughes' poem as her title, and also adopts the theme of the poem as the theme of her play.