The chief of the National Guard Bureau (CNGB) is the highest-ranking officer of the National Guard and the head of the National Guard Bureau. The position is a statutory office, held by a federally recognized commissioned officer who has served at least 10 years of federally recognized active duty in the National Guard; the Army National Guard or the Air National Guard. In a separate capacity as a member of the Joint Chiefs of Staff, the chief is a military adviser to the National Security Council, the Homeland Security Council, the secretary of defense, and the president on matters pertaining to the National Guard.

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.