Memoirs of the Nuttall Ornithological Club, Number 20. A history of the first 100 years of the A.O.U., highlighting the Union's activities and accomplishments, relating some to overall developments in the evolution of American natural science. Cambridge, Massachusetts: Published by the Club, With the support of the American Ornithologists' Union, 2016. Contents: Beginnings; By-Laws; The Auk, A Quarterly Journal of Ornithology; Classification and Checklists; Annual Meetings; Research and Awards in the AOU; Bird Protection; Special Projects; Patterns of Change in the AOU; Conclusions. Endnotes; Literature Cited. Appendices: Presidents, Vice Presidents, Secretaries, Treasurers, Editors; AOU Founders, 1883, and highlights of their careers; Annual Meetings of the AOU 1883-1982; Brewster Medals 1929-1982; Coues Awards 1972-1982; The 'Ten Year Index' of The Auk; Pertinent data of the Ornithological Monographs; Index.