The American Ornithological Society (AOS) is an ornithological organization based in the United States. The society was formed in October 2016 by the merger of the American Ornithologists' Union (AOU) and the Cooper Ornithological Society. Its members are primarily professional ornithologists, although membership is open to anyone with an interest in birds. The society publishes the two scholarly journals, Ornithology (formerly The Auk) and Ornithological Applications (formerly The Condor) as well as the AOS Checklist of North American Birds.
In 2013, the American Ornithologists' Union announced a close partnership with the Cooper Ornithological Society, including joint meetings, a centralized publishing office, and a refocusing of their respective journals to increase efficiency of research.