Field Manual (FM) 3-37, "Protection," provides doctrinal guidance for commanders and staffs who are responsible for planning and executing protection in support of full spectrum operations. It describes protection as both an element of combat power and as a warfighting function. FM 3-37 corresponds with Army operations doctrine introduced in the FM 3-0 capstone manual. As the Army keystone manual for protection, FM 3-37 will help commanders understand and visualize protection concepts and ideas and enable them to describe protection tasks and systems for integration into the operations process. FM 3-37 expands on the protection and combined arms terminology outlined in FM 3-0. It explains how protection can be achieved and applied through the combination and integration of reinforcement and complementary capabilities to preserve combat power or to protect personnel, physical assets, or information. This manual recognizes that protection has no direct antecedent from the former battlefield operating systems, so protection is realized in many ways. Therefore, the text introduces the five forms and five principles of protection to provide a context for battle command and a framework for task assignment: Forms of protection; Deterrence; Prevention; Active security; Passive defense; Mitigation; Principles of protection; Full-dimension; Integrated; Layered; Redundant; Enduring. FM 3-37 also introduces and explains the twelve Army tasks that comprise the protection warfighting function and describes how those tasks are realized and represented during full spectrum operations: Air and missile defense (AMD); Personnel recovery (PR); Information protection; Fratricide avoidance; Operational area security; Antiterrorism (AT); Survivability; Force health protection (FHP); Chemical, biological, radiological, and nuclear (CBRN) operations; Safety; Operations security (OPSEC); Explosive ordnance disposal (EOD). This manual affirms the composite risk management (CRM) process as the overarching process for integrating protection into Army operations and depicts a broad methodology for determining protection priorities from which specific decision support tools can nest. FM 3-37 provides guidance on how the protection cell within the division, corps, and Army headquarters is formed for protection planning, preparation, execution, and continuous assessment. Commanders should be aware that homeland defense and civil support operations in the continental United States (CONUS) are governed by a distinct set of laws and policies regarding the employment of forces, types of operations, and use of force. These laws and policies must be factored into determining the appropriate use of protection principles and tasks and systems for an operation in CONUS. This manual follows joint doctrine and introduces several ideas to provide a context for understanding protection within the military art and science of operations to achieve its purpose of preserving the force-personnel (combatant and noncombatant), physical assets, and information. FM 3-37 strives for a broad application of some universal concepts regarding protection and also integrates lessons learned from five years of combat operations.