Traumatic brain injury (TBI) is a continuing concern for military treatment facilities operated by the Department of Defense (DoD), the Veterans Health Administration (VHA), and civilian health care providers who deliver services to US active duty service members and veterans. This chapter underscores the clinical situation of 'polytrauma' as relevant to military and veteran populations given the high frequency of co-occurring disorders that are seen in military and veteran treatment environments. The phenomena of brain injury sustained in war are recorded in the historical literature as far back as wars have been documented. Blunt head trauma and penetrating head wounds occur due to the multiplicity of exposures that can occur in the war zone. The term 'concussion' is frequently used in reference to OEF/OIF/OND service members and veterans who experienced an event that leads to immediate concussive symptomatology and may be a result of various mechanical forces or, in the deployed setting, also due to blast-related forces.