The Unified Command Plan (UCP) and associated Combatant Commands (COCOMs) provide operational instructions and command and control to the Armed Forces and have a significant impact on how they are organised, trained and resourced - areas over which Congress has constitutional authority. The UCP is a classified executive branch document prepared by the Chairman of the Joint Chiefs of Staff and reviewed and updated every two years that assigns missions; planning, training, and operational responsibilities; and geographic areas of responsibilities to COCOMs. This book provides information on the history, mission, and operational considerations of the UCP and COCOMs with a focus on current issues and considerations.