Andrew J. Bacevich Jr. (/ˈbeɪsəvɪtʃ/, BAY-sə-vitch; born July 5, 1947) is an American historian specializing in international relations, security studies, American foreign policy, and American diplomatic and military history. He is a professor emeritus of international relations and history at the Boston University Frederick S. Pardee School of Global Studies. He is also a retired career officer in the Armor Branch of the United States Army, retiring with the rank of colonel. He is a former director of Boston University's Center for International Relations (from 1998 to 2005), now part of the Pardee School of Global Studies. Bacevich is the co-founder and president of the Quincy Institute for Responsible Statecraft.

Bacevich has been "a persistent, vocal critic of the U.S. occupation of Iraq, calling the conflict a catastrophic failure." In March 2007, he described George W. Bush's endorsement of such "preventive wars" as "immoral, illicit, and imprudent." His son, Andrew John Bacevich, also an Army officer, died fighting in the Iraq War in May 2007.

In July 2024, he signed an open letter against inviting Ukraine into NATO.

Bacevich was born in Normal, Illinois, the son of Martha Ellen (née Bulfer; later Greenis) and Andrew Bacevich Sr. His father was of Lithuanian descent, and his mother was of Irish, German, and English ancestry. Bacevich described himself as a "Catholic conservative."

He graduated from the United States Military Academy in 1969 and served in the United States Army during the Vietnam War, serving in Vietnam from the summer of 1970 to the summer of 1971.

Later he held posts in Germany, including in the 11th Armored Cavalry Regiment; the United States; and the Persian Gulf up to his retirement from the service with the rank of colonel in the early 1990s. His early retirement is thought to be a result of his taking responsibility for the Camp Doha (Kuwait) explosion in 1991 in command of the 11th Armored Cavalry Regiment. He holds a Ph.D. in American Diplomatic History from Princeton University, where his 1982 doctoral thesis was entitled American military diplomacy, 1898–1949: the role of Frank Ross McCoy. Bacevich taught at West Point and Johns Hopkins University before joining the faculty at Boston University in 1998.^{[citation needed]}

Bacevich initially published writings in a number of politically oriented magazines, including The Wilson Quarterly. He advocates for a non-interventionist foreign policy. His writings have professed a dissatisfaction with the Bush administration and many of its intellectual supporters on matters of U.S. foreign policy.

On August 15, 2008, Bacevich appeared as the guest of Bill Moyers Journal on PBS to promote his book, The Limits of Power. As in both of his previous books, The Long War (2007) and The New American Militarism: How Americans are Seduced by War (2005), Bacevich is critical of U.S. foreign policy in the post-Cold War era, maintaining the United States has developed an over-reliance on military power, in contrast to diplomacy, to achieve its foreign policy aims. He also asserts that policymakers in particular, and the U.S. people in general, overestimate the usefulness of military force in foreign affairs. Bacevich believes romanticized images of war in popular culture (especially films) interact with the lack of actual military service among most of the U.S. population to produce in the U.S. people a highly unrealistic, even dangerous notion of what combat and military service are really like.