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 and Ornithological Applications as well as the AOS Checklist of North American Birds. The American Ornithological Society claims the authority to establish standardized English bird names throughout North and South Americas.

The Nuttall Ornithological Club is the oldest ornithology organization in the United States.