The under secretary of defense for intelligence and security or USD(I&S) is a high-ranking civilian position in the Office of the Secretary of Defense (OSD) within the U.S. Department of Defense (DoD) that acts as the principal civilian advisor and deputy to the secretary of defense (SecDef) and deputy secretary of defense (DepSecDef) on matters relating to military intelligence and security. The under secretary is appointed as a civilian by the president and confirmed by the Senate to serve at the pleasure of the president.

The United States Department of Defense is an executive branch department of the federal government of the United States charged with coordinating and supervising all agencies and functions of the U.S. government directly related to national security and the United States Armed Forces. As of June 2022, the U.S. Department of Defense is the largest employer in the world, with over 1.34 million active-duty service members, including soldiers, marines, sailors, airmen, and guardians. The Department of Defense also maintains over 778,000 National Guard and reservists, and over 747,000 civilians bringing the total to over 2.87 million employees. Headquartered at the Pentagon in Arlington County, Virginia, just outside Washington, D.C., the Department of Defense's stated mission is to provide "the military forces needed to deter war and ensure our nation's security".