No one captivated Katherine S. Dreier more than Marcel Duchamp. From the moment the painter-collector met the Frenchman in the fall of 1916 until her death in March 1952, she remained his intrepid champion, generous benefactor, and loyal collaborator. In April 1920, Dreier, Duchamp, and Man Ray founded the Société Anonyme, Inc., the first museum of modern art in the United States. For thirty years, the Société Anonyme presented numerous groundbreaking exhibitions and underwrote several important publications exploring what Dreier described as the “new tendencies” in modern art. Étant donné Marcel Duchamp is proud to devote our ninth volume to the long and rich friendship between Dreier and Duchamp. The issue commences with an interview with Monique Wiedel, whose mother, a painter and collector, was a close friend of Dreier’s and a member of the Société Anonyme. Following this are selections from Duchamp’s and Dreier’s lengthy correspondence as well as from Dreier’s published and unpublished writings about her friend. In addition to a major historical overview with the many activities of the Société Anonyme, the issue features a major study of the Large Glass, which Dreier owned, a French translation of a small book about the Large Glass that Dreier and Matta published in 1944, excerpts from texts on and by the Société Anonyme, and much more. Over 280 photographs and documents, many of them unpublished, illustrate these and the numerous other articles comprising Étant donné Marcel Duchamp n° 9.