Army Doctrine Publication (ADP) 4-0, Sustainment, is the Army's doctrine for sustainment of Army missions. This principle level doctrine focuses on the three elements of sustainment: logistics, personnel services, and health service support. The principal audience for ADP 4-0 is all members of the profession of arms. Commanders and staffs of Army headquarters serving as joint task force or multinational headquarters should also refer to applicable joint or multinational doctrine concerning the range of military operations and joint or multinational forces. Trainers and educators throughout the Army will also use this manual. Commanders, staffs, and subordinates ensure their decisions and actions comply with applicable U.S., international, and, in some cases, host nation laws and regulations. Commanders at all levels ensure their Soldiers operate in accordance with the law of war and the rules of engagement.