- A. Franklin Kibler papers, 1943/19526
- A. Patrick L. Prest, Jr. papers, 1941/20141
- A. Rufus Tonelson Papers, 1922/19752
- A. Willis Robertson Papers, 1921/1988, bulk 1946/196612
- Abraham Anson papers, 1939/20056
- Adele Blow Chatfield-Taylor family papers, 1899/19772
- Adele Goodman Clark papers, 1849/19784
- Administrative Management Society records, 1941/1987, bulk 1941/19871
- Adolphus DeBussey, Soldier, Civil War Letters, 1861/1998, bulk 1861/18711
- Advisory Committee Research Collection, 1772/20174
- Alan Clarke Railroad Research Papers, 1861/20122
- Albert J. Wasserman Papers, 1925/20031
- Albert L. Sturm Papers, 1904/19884
- Alberta Pfeiffer Architectural Collection, 1929/19762
- Alexander Haight family collection, 1764/19761