Although documentation that war inflicts psychological casualties dates back to the American Civil War and earlier, most research began after the Vietnam conflict, when studies focused on post-traumatic stress disorder (PTSD). With ongoing conflicts in Iraq and Afghanistan, there has been significant research to illuminate the epidemiology of war-related psychological casualties. Significant findings include an appreciation for the role combat plays in the development of mental disorders, including PTSD and traumatic brain injury (TBI). Recent research has endeavoured to understand and improve psychological resilience to temper potentially adverse mental health effects of military service in the theatre of combat operations. Over 2 million US service members have now deployed and returned over 3 million times to the Iraq and Afghanistan conflicts. Mental health providers in the Departments of Defense and Veterans Affairs healthcare systems have consequently observed steep increases in mental health service use among these personnel. The Departments have responded aggressively to bolster staffing levels, increase capacity, improve available services, and anticipate future needs. Scientists and clinicians continue efforts to understand the determinants, prevention, recognition, and treatment of combat-related mental disorders.