The primary objective of the military health system, which includes the Defense Department’s hospitals, clinics, and medical personnel, is to maintain the health of military personnel so they can carry out their military missions and to be prepared to deliver health care during wartime. The military health system also covers dependents of active duty personnel, military retirees and their dependents, including members of the reserve components. This book provides an overview of how the military health system is structured; a description of TRICARE and who is eligible; the costs of military health care to beneficiaries; the relationship of TRICARE to Medicare; and whether the Affordable Care Act (ACA) affects TRICARE.