The United States Coast Guard (USCG), founded in 1790, is a military branch of the United States involved in maritime law, mariner assistance, and search and rescue, among other duties of coast guards elsewhere. One of the seven uniformed services of the United States, and the smallest armed service of the United States, its stated mission is to protect the public, the environment, and the United States economic and security interests in any maritime region in which those interests may be at risk, including international waters and America's coasts, ports, and inland waterways.

USCG has a broad and important role in homeland security, law enforcement, search and rescue, marine environmental pollution response, and the maintenance of river, intracoastal and offshore aids to navigation (ATON).

The Coast Guard has the oldest ) Auxiliary, founded in 1939 as the Coast Guard Reserve, with approximately 30,000 uniformed volunteer members serving in all roles except direct law enforcement and military.

The Coast Guard's motto is Semper Paratus, meaning "Always Ready".

The Coast Guard's roots lie in the Revenue Cutter Service, which was founded on August 4, 1790 as part of the Department of the Treasury. An act of the U.S. Congress created the Coast Guard in 1915, with the merger of the Revenue Cutter Service and the United States Lifesaving Service. The United States Lighthouse Service was merged into the Coast Guard in 1939. The legal basis for the Coast Guard is Title 14 of the United States Code, which states: "The Coast Guard as established January 28, 1915, shall be a military service and a branch of the armed forces of the United States at all times." Upon the declaration of war or when the President directs, the Coast Guard operates under the authority of the Department of the Navy. The Coast Guard later moved to the Department of Transportation in 1967, and on February 25, 2003 it became part of the Department of Homeland Security.