Just Kids, a memoir written by American musician Patti Smith and winner of the 2010 National Book Award for Nonfiction, documents Smith's relationship with the photographer Robert Mapplethorpe. The memoir begins in Smith and Mapplethorpe's childhood, and moves through their young adulthood in the late 1960s and 1970s in New York City. Just Kids begins and ends with Smith learning of Mapplethorpe's death from AIDS in 1989. Raised in "rural South Jersey" (23), the oldest of three children, Smith feels she wants to be an artist from a young age. Though she doesn’t mind "the misery of a vocation" (12) to art, her home is "hardly pro-artist" (23). At age 19, Smith boards a bus to New York City, hoping to connect with friends at the Pratt Institute. Instead, Smith meets Robert Mapplethorpe, a 19-year-old boy, raised in a conservative, Catholic household in Long Island. Mapplethorpe has known he was an artist since childhood; he is "a natural draftsman" (13) who also made jewelry for his mother. Their serendipitous meeting at the former house of Smith's friends initiates Mapplethorpe and Smith into a lifelong friendship. 

In the summer of 1967, Mapplethorpe helps Smith get out of an awkward date with a customer at the bookstore where she works. Smith spends the night with Mapplethorpe, looking at his artwork and talking about art. From that night on, Smith and Mapplethorpe don't leave "each other's side save to go to work" (42). They move into a crummy apartment, which they salvage and turn into a livable space, with room for each of them to work on their art. Smith writes and draws, while Mapplethorpe works on collages and small installations. Though so broke they often shared a sack of stale cookies for dinner, the two are happy. They support each other's goals of making art for a living, though Smith sometimes thinks it "indulgent to add to the glut unless one offer[s] illumination" (65). Mapplethorpe, on the other hand, "never seem[s] to question his artistic drives" (65) and continuously encourages Smith. While Smith sees making art as its own reward, Mapplethorpe wants "nothing more than to make it on his own" (223) through his art alone.

As their artistic journeys continue, the two become closer then drift apart. They collaborate on each other's work, serving as muse and critic to one another. When Mapplethorpe begins to question his sexuality, believing he may be homosexual, he first pushes Smith away, becoming taciturn and saying he'll "turn homosexual" (74) if she doesn't go with him on his trip to San Francisco. Mapplethorpe contracts gonorrhea in San Francisco and, upon returning to New York, draws himself closer to Smith, making a vow not to leave her side until they can stand on their own. They move to the Chelsea Hotel, a haven for artists, where Smith and Mapplethorpe meet several key players in their future as artists. Eventually, Mapplethorpe and Smith get their own apartments but continue working side-by-side, as they had before. Sam Wagstaff, a wealthy older gentleman and "quintessential patron" (234), supports Mapplethorpe financially and becomes his lover. Smith, with the encouragement of Mapplethorpe and others, publishes a few books of her poems, and begins performing them at venues. Later, after adding first a guitar then a backing band, Smith channels her performance "bravado" (165) and begins to play rock-and-roll shows. She records her debut album, Horses, at Jimi Hendrix's Electric Ladyland studios and releases it on Arista Records in 1975. In 1978, Smith moves to Detroit to live with her husband, the guitarist Fred Sonic Smith. In 1986, Mapplethorpe receives his AIDS diagnosis. In the last three years of Mapplethorpe's life, Smith and her family travel to New York frequently as she records her Dream of Life album and Mapplethorpe photographs Smith several times, including the picture on that album's cover.