The Massachusetts National Guard is the National Guard component for the Commonwealth of Massachusetts. Founded as the Massachusetts Bay Colonial Militia on December 13, 1636, it contains the oldest units in the United States Army. What is today's Massachusetts National Guard evolved through many different forms. Originally founded as a defensive militia for Puritan colonists in the Massachusetts Bay Colony, the militia evolved into a highly organized and armed fighting force. The Massachusetts militia served as a central organ of the New England revolutionary fighting force during the early American Revolution and a major component in the Continental Army under George Washington.

The National Guard is a state-based military force that becomes part of the U.S. military's reserve components of the U.S. Army and the U.S. Air Force when activated for federal missions. It is a military reserve force composed of National Guard military members or units of each state and the territories of Guam, the Virgin Islands, Puerto Rico, and the District of Columbia, for a total of 54 separate organizations. It is officially created under Congress's Article 1 Section 8 ability to "raise and support armies". All members of the National Guard are also members of the organized militia of the United States as defined by 10 U.S.C. § 246. National Guard units are under the dual control of state governments and the federal government.