Alfred Stieglitz's gallery was called 291.
The gallery took its name from its address at 291 Fifth Avenue in New York City. Stieglitz opened it in 1905 as the Little Galleries of the Photo-Secession, a space initially associated with the Photo-Secession movement and the promotion of artistic photography. It became known simply as 291.
The gallery introduced American audiences to European modern art, including works by artists such as Pablo Picasso, Henri Matisse, and Constantin Brâncusi. Stieglitz also used it to present the work of American artists, including Georgia O'Keeffe. Her first exhibitions there began in 1916, after Anita Pollitzer showed Stieglitz photographs of O'Keeffe's drawings.
291 closed in 1917, but Stieglitz continued exhibiting O'Keeffe at later venues. Those later spaces included the Intimate Gallery and An American Place, so the gallery name should not be confused with every New York venue associated with her career.