The Chief of the National Guard Bureau (CNGB) is the head of the National Guard Bureau, which is a joint activity of the Department of Defense, and is a member of the Joint Chiefs of Staff. The Chief of the National Guard Bureau is the highest-ranking officer in the National Guard of the United States; which is a joint reserve component of the United States Army and the United States Air Force. The CNGB serves as the principal advisor to the Secretary of Defense, through the Chairman of the Joint Chiefs of Staff, on matters involving non-federalized National Guard forces and on other matters as determined by the Secretary of Defense. The CNGB also serves as the principal adviser to the Secretary of the Army, Secretary of the Air Force, the Chief of Staff of the Army, and the Chief of Staff