The Green Mountain Boys were a militia organization first established in the 1760s in the territory between the British provinces of New York and New Hampshire, known as the New Hampshire Grants (which later became the state of Vermont). Headed by Ethan Allen and members of his extended family, they were instrumental in resisting New York's attempts to control the territory, over which it had won de jure control in a territorial dispute with New Hampshire.

When these disputes led to the formation of the Vermont Republic in 1777, the Green Mountain Boys became the state militia. Some companies served in the American Revolutionary War, including notably when the Green Mountain Boys led by Ethan Allen captured fort Ticonderoga on Lake Champlain on May 10, 1775; the invasion of Canada in 1775; and the battles at Hubbardton and Bennington in 1777.

Following Vermont's admission to the Union in 1791, the original organization essentially disbanded. The Green Mountain Boys mustered again during the War of 1812, the Civil War, and the Spanish-American War. Today it is the informal name of the Vermont National Guard which comprises both the Army and Air National Guards.