Patriots' Day is an annual event, formalized as a legal holiday or a special observance day in six U.S. states, commemorating the battles of Lexington, Concord, and Menotomy, the inaugural battles of the American Revolutionary War. The holiday occurs on the third Monday of April each year, with celebrations including battle reenactments and the Boston Marathon.

The Battles of Lexington and Concord was the first major military campaign of the American Revolutionary War, resulting in an American victory and outpouring of militia support for the anti-British cause. The battles were fought on April 19, 1775, in Middlesex County, Province of Massachusetts Bay, within the towns of Lexington, Concord, Lincoln, Menotomy, and Cambridge. They marked the outbreak of armed conflict between the Kingdom of Great Britain and Patriot militias from America's thirteen colonies.