The American Ophthalmological Society (AOS) is a medical society of ophthalmologists and the second oldest specialty medical society in the United States, after the New York Ophthalmological Society (founded on March 7, 1864). It was founded on June 7, 1864 by 18 physicians, including Henry Noyes, D. B. St. John Roosa, and Edward Delafield (its first president and also one of the founders of the New York Eye and Ear Infirmary). The society is now based in San Francisco, California. A collection of the society's papers are held at the National Library of Medicine.