TP 525-4-1 describes the broad capabilities the Army will require to sustain multi-domain battle and cross-domain maneuver with joint, interorganizational, and multinational partners during 2020-2040. The ideas presented have been integrated with the evolving estimates of the operational environment; and joint and Army strategic guidance. This functional concept will lead force development and employment efforts by establishing a common framework to guide developments for sustaining future Army operations. Sustainment is the provision of logistics, personnel services, and health service support to maintain operations until mission accomplishment. The sustainment warfighting function includes the related tasks and systems that provide support and services to ensure freedom of action, extend operational reach, and prolong endurance. The endurance of Army forces is primarily a function of their sustainment which determines the scale and duration of operations essential to retaining and exploiting the initiative. The Army sustains operations by employing integrated processes involving people and systems to deliver support and services. Strategically, sustainment forces integrate joint, interorganizational, and multinational partners to build capability, train, and account for a combat ready Army for the joint force commander (JFC). Operationally, sustainment forces provide support to and assist with force deployment and sustain operations to enable freedom of action and operational reach across multiple theaters. Tactically, sustainment forces deliver supplies and services to the warfighter to enable cross-domain maneuver and prolong endurance. The AOC recognizes that Army forces will be essential components of joint operations to create sustainable political outcomes while defeating enemies and adversaries who will challenge U.S. advantages in all domains: land, air, maritime, space, and cyberspace. Joint operations are critical to cope with such complexity and the Army's contribution must provide unique capabilities and multiple options to the President, the Secretary of Defense, and geographic combatant commanders. These capabilities include tailorable and scalable combinations of special operations and conventional forces, regionally aligned and globally responsive combined arms teams, and foundational theater capabilities to enable joint combined arms operations and winning in a complex world.