This United States Army manual, Army Techniques Publication ATP 3-90.20 Regional Support Group September 2024, establishes regional support group (RSG) doctrine. It also aligns and nests with joint and Army doctrine. To comprehend the doctrine contained in this publication, readers must first understand the nature of operations as described in JP 3-0, ADP 3-0, and FM 3-0. In addition, readers must fully understand the fundamentals of the operations process contained in ADP 5-0, the principles of mission command described in ADP 6-0, Armies, corps, and division operations in FM 3-94, the execution of defense support of civil authorities (DSCA) discussed in JP 3-28, ADP 3-28, and ATP 3-28.1, the protection tasks discussed in ADP 3-37, theater Army operations described in ATP 3-93, and the base camp life cycle described in ATP 3-37.10.In addition, readers should understand ADP 1 to understand the organization and doctrinal principles of the Army Profession and know how the moral principles of the Army Ethic apply to all operations, decisions, and actions. The principal audience for ATP 3-90.20 is commanders and staffs at the division, corps, and theater army echelons, RSGs, and units in a command or support relationship with RSGs primarily tasked with conducting base camp management, base security and defense operations, DSCA operations, joint reception, staging, onward movement, and integration (RSOI), and mobilization force generation installation (MFGI) operations. Army Civilians, trainers, educators, and contractors will also use this publication. Leaders and staff sections within units that employ a RSG or may operate under a RSG also use this publication. Furthermore, unified action partners and higher headquarters commanders and staff use this publication to guide their actions on RSG employment.