Bernard Bailyn (born September 9, 1922) is an American historian, author, and academic specializing in U.S. Colonial and Revolutionary-era History. He has been a professor at Harvard University since 1953. Bailyn has won the Pulitzer Prize for History twice (in 1968 and 1987). In 1998 the National Endowment for the Humanities selected him for the Jefferson Lecture. He was a recipient of the 2010 National Humanities Medal. He is married to MIT Professor of Management Lotte Bailyn (née Lotte Lazarsfeld) and is the father of Yale astrophysicist Charles Bailyn and Stony Brook Linguist John Bailyn.
He has specialized in American colonial and revolutionary-era history, looking at merchants, demographic trends, Loyalists, international links across the Atlantic, and especially the political ideas that motivated the Patriots. He is best known for studies of republicanism and Atlantic history that transformed the scholarship in those fields. He was elected a Fellow of the American Academy of Arts and Sciences in 1963.