Fountain is Marcel Duchamp's most publicized readymade existing primarily—if not exclusively—as a single photograph by Alfred Stieglitz published in the Dada review, The Blind Man, in the Spring of 1917. The image describes a porcelain urinal rotated 90 degrees, signed "R. Mutt 1917," and placed on a pedestal in front of Marsden Hartley's painting The Warriors. This photograph, rather than any physical object, is the core provocation of the readymade sculpture as Duchamp defined his readymade in terms of "an everyday object raised to the dignity of a work of art by the artist's act of choice." For its presentation in The Blind Man, Duchamp altered the urinal 90 degrees from its usual positioning. Following its removal from the Society of Independent Artists inaugural juried exhibition, where it was rejected by the hanging committee-- despite the society's open policy-- as sculpture, Duchamp took Fountain to Stieglitz' 291 gallery, had it photographed, and allegedly sold it to the collector Walter Arensberg, who lost it.

Technically, Fountain was not rejected by the committee, since Society rules stated that all works would be accepted from artists who paid the fee. The work was never placed in the show area but no evidence proves the urinal's actual delivery to the Society of Independent Artists either. There is also no record of the original ever having been exhibited prior to its authorization as replica, in an edition of eight by the art dealer Arturo Schwarz, under the close supervision of Duchamp, shortly before Duchamp's death in 1968. Contemporary accounts rely heavily on writings in The Blind Man, including Louise Norton's presentation of Fountain's submission and rejection, and on Duchamp's recollection of the real event.

21st century art historians presume the sculpture to have been lost or destroyed. Despite this, or because of it, Fountain is regarded by art historians and theorists as a major landmark in the 20th-century American avant-garde. In the late 1990's and early 2000's, historian Rhonda Roland Shearer, with the late paleontologist Stephen Jay Gould, conducted extensive analysis of Fountain using historical prototypes, museum archives, and period plumbing catalogs. Their experiments show that no commercially manufactured urinal from 1917 matches the proportions, details, and perspective in Stieglitz's photograph—making it impossible to capture such an object from the precise angle and with the observed features using standard photography. The idea that the Steiglitz image is more likely a composite (assembled from multiple photographs at different scales/angles) than the object is a factory error, or the result of Duchamp's staged manipulation, has been met with as much controversy as Fountain itself. An empirical comparison of the 1917 image to the surviving replicas shows Duchamp's readymade to be non-obvious. Others maintain that the original work was by the female artist Elsa von Freytag-Loringhoven who had submitted it to Duchamp as a friend.

Fountain is included in the Marcel Duchamp catalogue raisonné by Arturo Schwarz; The complete works of Marcel Duchamp (number 345).