FM 4-0 is the Army's keystone manual for sustainment. Its purpose is to provide authoritative doctrine for the sustainment of forces in full spectrum operations. It expands on sustainment doctrine introduced in FM 3-0 to incorporate a broader approach to sustaining the fighting force. The intent of this FM is to describe how sustainment builds and maintains combat power, supports strategic and operational reach, and enables endurance. This FM establishes how sustainment operations are integrated and synchronized into the overall operations process - plan, prepare, execute, and assess. In accordance with FM 3-0, the terms combat arms, combat support (CS), and combat service support (CSS) are no longer used as Army doctrine lexicon. The term sustainment covers many of the functions, tasks, and organizations formerly described under CSS although there are some differences which will be discussed in this FM. Sustainment includes the major sub-functions logistics, personnel services, and health services support. Sustainment as defined and discussed in this FM is compatible with the joint function, sustainment. FM 4-0 has five chapters and two appendices. It addresses the operational environment and modular force sustainment organizations. It introduces the roles and functions of the generating and operating forces. It explains the art of battle command from a sustainment commander's perspective. Finally, it explains sustainment as one of six warfighting functions (WFF) and presents doctrine for how sustainment is planned, prepared, executed, and continuously assessed. - Chapter 1 is the introduction to sustainment. It covers the principles of sustainment and the sustainment WFF. - Chapter 2 covers the roles and responsibilities of organizations providing sustainment in support of unified action. It links Army sustainment to joint sustainment operations. It covers commands, organizations, and agencies that provide sustainment including Joint organizations, Army Generating Forces, and Operating Forces. It also discusses sustainment to multinational operations. - Chapter 3 covers command and control. It discusses battle command from a sustainment perspective. It also discusses modular force sustainment organization and their relationships to Army operations. - Chapter 4 discusses the integration of sustainment into operations. It explains how sustainment considerations are integrated into the operations process. - Chapter 5 provides a more detailed discussion on the major functional elements of sustainment. - Appendix A contains details on the various information systems. - Appendix B lists the references for multinational Standardization Agreements (STANAGs) impacting on the sustainment of forces. FM 4-0 applies to the Active Army, the Army National Guard/Army National Guard of the United States, the United States Army Reserve unless otherwise stated, and military and civilian leaders at all levels of war. It provides guidance to our joint and multinational partners on how Army sustainment may support joint and multinational operations. It links Army sustainment doctrine to joint sustainment doctrine as expressed in joint doctrinal publications, specifically, JP 1-0 series and JP 4-0 series manuals.