The Defense Intelligence Agency (DIA) is an intelligence agency and combat support agency of the United States Department of Defense, specializing in defense and military intelligence.

A component of the Department of Defense (DoD) and the Intelligence Community (IC), DIA informs national civilian and defense policymakers about the military intentions and capabilities of foreign governments and non-state actors. It also provides intelligence assistance, integration and coordination across uniformed military service intelligence components, which remain structurally separate from DIA. The agency's role encompasses the collection and analysis of military-related foreign political, economic, industrial, geographic, and medical and health intelligence. DIA produces approximately one-quarter of all intelligence content that goes into the President's Daily Brief.

DIA's intelligence operations extend beyond the zones of combat, and approximately half of its employees serve overseas at hundreds of locations and in U.S. embassies in 140 countries. The agency specializes in the collection and analysis of human-source intelligence (HUMINT), both overt and clandestine, while also handling U.S. military-diplomatic relations abroad. DIA concurrently serves as the national manager for the highly technical measurement and signature intelligence (MASINT) and as the Defense Department manager for counterintelligence programs. The agency has no law enforcement authority, contrary to occasional portrayals in American popular culture.

DIA is a national-level intelligence organization that does not belong to a single military element or within the traditional chain of command, instead answering to the Secretary of Defense directly through the Under Secretary of Defense for Intelligence. Three-quarters of the agency's 17,000 employees are career civilians who are experts in various fields of defense and military interest or application; and although no military background is required, 48% of agency employees have some past military service. DIA has a tradition of marking unclassified deaths of its employees on the organization's Memorial Wall.

Established in 1961 under President John F. Kennedy by Defense Secretary Robert McNamara, DIA was involved in U.S. intelligence efforts throughout the Cold War and rapidly expanded, both in size and scope, after the September 11 attacks. Because of the sensitive nature of its work, the spy organization has been embroiled in numerous controversies, including those related to its intelligence-gathering activities, to its role in torture, as well as to attempts to expand its activities on U.S. soil.