The history of the U.S. Coast Guard and its predecessor agencies dates from 1790, with missions in both domestic and international waters. The service has provided aids to navigation, enforcement of maritime laws, environmental protection, search and rescue, immigration and narcotics interdiction, maritime safety assistance, port security, natural disaster response and national defense missions, including overseas with other U.S. armed forces and federal and state public safety agencies.

The Service has operated under the Department of the Treasury, the Department of Transportation and, since 2003, the Department of Homeland Security. Its maritime mission regions have included Arctic and Antarctic waters, inland and coastal U.S. waterways and the seas and oceans of the world. This history describes how the Coast Guard has manifested its legacy and motto, Semper Paratus (Always Ready), in changing conditions under each of its leaders.