Thomas Andrew Bailey (December 14, 1902 – July 26, 1983) was a professor of history at his alma mater, Stanford University, and wrote many historical monographs on diplomatic history, as well as the widely used American history textbook, The American Pageant. He was known for his witty style and clever terms he coined, such as "international gangsterism." He popularized diplomatic history with his entertaining textbooks and lectures, the presentation style of which followed Ephraim Douglass Adams. Bailey contended foreign policy was significantly affected by public opinion, and that current policymakers could learn from history.

Bailey received his Bachelor of Arts in 1924, Master of Arts in 1925, and Doctor of Philosophy in 1927, all from Stanford University, where he was also elected to Phi Beta Kappa. His doctoral work was in U.S. political history. He switched his emphasis towards diplomatic history while teaching at the University of Hawaiʻi.

After three years at the University of Hawaiʻi, he taught American history for nearly 40 years at Stanford and also served as a visiting professor at Harvard University, Cornell University, the University of Washington, and the National War College in Washington, D.C. He retired in 1968.

Bailey authored a number of articles in the 1930s that indicated the historical techniques he would use throughout his career. While not groundbreaking, they remain noteworthy for the care with which Bailey systematically overturned received myths about U.S. diplomatic history by a careful reexamination of the underlying sources. His first book was a study of the diplomatic crisis over racial issues between the United States and Japan during the Theodore Roosevelt administration.

He delivered the Albert Shaw Lectures on Diplomatic History at Johns Hopkins University on the Wilson administration's policy towards neutral nations in 1917-1918, later published in 1942. While the impact of public opinion on the making of foreign policy was a theme that ran through most of his works, he laid it out most clearly in The Man in the Street, published in 1948.^{[citation needed]}

Perhaps the harshest attack on Wilson's diplomacy came from Bailey in two books that remain widely cited by scholars, Woodrow Wilson and the Lost Peace (1944) and Woodrow Wilson and the Great Betrayal (1945), Bailey:

He trained more than 20 doctoral students in his career.

He was married to Sylvia Dean, daughter of a former University of Hawaiʻi president.