This publication provides doctrine for the Army Health System (AHS) in support of the modular force. The AHS is the overarching concept of support for providing timely AHS support to the tactical commander. It discusses the current AHS force structure modernized under the Department of the Army (DA)-approved Medical Reengineering Initiative and the Modular Medical Force that is designed to support the brigade combat teams (BCTs) and echelons above brigade (EAB) units. As the Army's AHS doctrine statement, this publication identifies medical functions and procedures that are essential for operations covered in other Army Medical Department (AMEDD) proponent manuals. This publication depicts AHS operations from the point of injury, illness, or wounding through successive roles of care within the area of operations (AO) and evacuation to the continental United States (CONUS)-support base. It presents a stable body of operational doctrine rooted in actual military experience and serves as a foundation for the development of AMEDD proponent manuals on how the AHS supports unified land operations. The AHS mission falls within two warfighting functions: sustainment and protection. To clearly delineate the two AHS missions of health service support (HSS) and force health protection (FHP), this publication is divided into three parts. Part One, AHS, provides a holistic view of the entire AHS and the complexities and interdependence of each medical function in successfully accomplishing the AMEDD's mission to conserve the fighting strength. This part of the manual describes and provides operational guidance on the AHS's EAB mission command headquarters, as well as the medical aspects of the Law of Land Warfare. Part Two, HSS, discusses the three mission sets of casualty care, medical evacuation, and medical logistics (MEDLOG). Casualty care encompasses all of the medical functions involved with direct patient care activities to include diagnostic medical laboratories, while medical evacuation and MEDLOG are separate medical functions. Part Three, FHP, encompasses preventive medicine, veterinary services, all of the preventive aspects of combat and operational stress control (COSC) and dental services, and area medical laboratory (AML) including the testing of suspect biological and chemical warfare agent specimens and samples. This publication is for use by commanders and their staffs and command surgeons. It is to be used as a guide in obtaining, as well as providing, AHS in an AO. Information in this publication is applicable to decisive actions in support of unified land operations. It is compatible with the Army's sustainment and protection doctrine and is in agreement with Joint Publication (JP) 4-02. Due to the nature of the medical profession which is highly regulated throughout both the civilian and military communities, AMEDD doctrine is heavily influenced by- United States and international law. Policy guidance in the form of Army regulations (ARs) and Department of Defense (DOD) policy promulgated in the form of DOD directives (DODD) and instructions (DODI) and other documents. Medical standards established by civilian organizations (such as the Joint Commission on the Accreditation of Health Care Organizations). Technical guidance from both military and civilian organizations charged with medical/scientific oversight responsibilities. Throughout this publication, as appropriate, reference is made to the major policy guidance impacting the specific topic."