The United States Department of Defense, abbreviated as DoD or DOD and sometimes called the Defense Department, is a civilian Cabinet organization of the United States government. The Department of Defense controls the U.S. military and is headquartered at The Pentagon. It is headed by the Secretary of Defense, The Department of Defense is based in The Pentagon in Arlington County, Virginia outside Washington, DC, across the Potomac River. It was created by combining the War Department (founded in 1789) with the Navy Department (founded in 1798; formerly the Board of Admiralty, founded in 1780), and the newly created Department of the Air Force. The department was formed in order to reduce interservice rivalry which was believed to have reduced military effectiveness during World War II. It includes the Army, Navy, Air Force, Marines, as well as non-combat agencies such as the National Security Agency and the Defense Intelligence Agency. In wartime, the Department of Defense also has authority over the Coast Guard; in peacetime, that agency is under the control of the Department of Homeland Security. Prior to the creation of DHS, the Coast Guard was under the control of the Department of Transportation. The Coast Guard has not been formally militarized since World War II, although it has participated in various military and law enforcement operations over the years.

An American bald eagle with wings displayed horizontally grasping three crossed arrows and bearing on its breast a shield of thirteen pieces Argent and Gules, a chief Azure. Above the eagle an arc of thirteen stars with alternating rays. Below the eagle a wreath of laurel to dexter and olive to sinister. On an encircling band the inscription "DEPARTMENT OF DEFENSE" at the top and "UNITED STATES OF AMERICA" at the bottom. When illustrating the seal in color, the background will be medium blue; the eagle and wreath proper; the arrows, stars and rays yellow/gold. The encircling band will be dark blue with yellow/gold edges and letters in white.

Symbolism: The American bald eagle, long associated with symbolism representing the United States of American and its military establishment, has been selected as an emblem of strength. The eagle is defending the United States, represented by the shield of thirteen pieces. The thirteen pieces are joined together by the blue chief, representing the Congress. The rays and stars above the eagle signify glory, while the three arrows are collectively symbolic of the three component parts of the Department of Defense. The laurel stands for honors received in combat defending the peace represented by the olive branch.

Background: The seal was originally approved on 8 October 1947, by the President for the National Military Establishment. The designation was changed to Department of Defense on 15 August 1949.