PAM 4-01 is the Army’s pillar 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 PAM 3-00 (Army Operations) to incorporate broader and specific approaches to sustaining the fighting force. This manual describes how sustainment builds and maintains Army power, supports strategic and operational reach, and enables endurance. This also establishes how sustainment operations are integrated and synchronized into the overall operations process – plan, prepare, execute, and assess.        The purpose of this manual is to provide policies and guidelines for the conduct of Army sustainment operations and to provide Army personnel in all units of the Philippine Army a guide in the performance of their duties, functions and responsibilities as sustainment personnel or not.        This manual discusses the nature of sustainment, addresses the operational environment and modular force sustainment organizations. It also explains the sustainment functions and how these functions are operationalize to support Army operations. It also introduces the roles and functions of the generating and operating forces. It explains the art of battle command from a sustainment commander’s perspective. It also explains sustainment warfighting function (WFF) and presents doctrine on how sustainment is planned, prepared, executed, and continuously assessed.        In accordance with PAM 3-00, the terms combat arms (CA), combat support (CS), and combat service support (CSS) are no longer used as Army doctrine terms. The term sustainment covers many of the functions, tasks, and organizations previously described under the former CSS manual although there are some differences which will be discussed in this manual. Sustainment includes the major areas such as logistics, personnel services, and health services support. Sustainment as defined and discussed in this manual is compatible with the joint function sustainment.        This manual is also a formal expression of military knowledge and thought, that the Army accepts as being relevant at a given time, which covers the nature of sustainment for the military operations during conflict, its preparation and the method of engaging in conflict to achieve success. This is descriptive rather than prescriptive, requiring judgement in application. It does not establish dogma nor provide a checklist of procedures, but is rather an authoritative guide, describing how the army thinks about sustainment, not how to sustain. As such, it attempts to be definitive enough to guide military sustainment activity, yet versatile enough to accommodate a wide variety of situations.   This document therefore would like to present this emerging sustainment doctrine for testing, ratification, and adoption not only by the Philippine Army leadership, but down to the Philippine Army’s least ranked soldier as well.