More than anything else, Just Kids is an artistic coming-of-age story about both Patti Smith and Robert Mapplethorpe. From childhood, both Smith and Mapplethorpe feel drawn towards creative expression. Smith dreams of "meeting an artist to love and support and work with side by side" (12)—something she later finds in Mapplethorpe. For Smith, the urge to express herself is her "strongest desire" (6) and she achieves this by drawing, dancing, and writing poems. Mapplethorpe draws and crafts jewelry for his mother. Mapplethorpe's father, a conservative middle-class Catholic, wants his son to study "commercial art" (6) and use his skills for practical aims. After meeting each other as young adults in New York City, Smith and Mapplethorpe enter into a codependent relationship in which they act as each other's muses. Convinced that nothing matters more than their dedication to art, Smith and Mapplethorpe are willing to work menial jobs and live "demoralized by hunger" (37) to support their art. 

Throughout their struggles to find themselves and find success as artists, Mapplethorpe maintains "absolute confidence in his work and in" (47) Smith. Mapplethorpe orients himself towards making art in order to make money, while Smith has "a more romantic view of the artist's life and sacrifices" (57) such that "committing to great art is its own reward" (57).