Military medical care is a congressionally authorized entitlement that has expanded in size and scope since the late 19th century. Chapter 55 of Title 10 U.S. Code, entitles certain health benefits to military personnel, retirees, and their families. These health benefits are administered by a Military Health System (MHS). The primary objectives of the MHS, which includes the Defense Department's hospitals, clinics, and medical personnel, are (1) to maintain the health of military personnel so they can carry out their military missions and (2) to be prepared to deliver health care during wartime. Health care services are delivered through either Department of Defense (DOD) medical facilities, known as military treatment facilities (MTFs) as space is available, or through civilian health care providers. As of 2017, the MHS operates 681 MTFs, employs nearly 63,000 civilians and 84,000 military personnel, and serves 9.4 million beneficiaries across the United States and in overseas locations. Since 1966, civilian care for millions of retirees, as well as dependents of active duty military personnel and retirees, has been provided through a program still known in law as the Civilian Health and Medical Program of the Uniformed Services (CHAMPUS), more commonly known as TRICARE. TRICARE has three main benefit plans: a health maintenance organization option (TRICARE Prime), a preferred provider option (TRICARE Select), and a Medicare supplement option (TRICARE for Life) for Medicare-eligible retirees. Other TRICARE plans include TRICARE Young Adult, TRICARE Reserve Select, and TRICARE Retired Reserve. TRICARE also includes a pharmacy program and optional dental and vision plans. Options available to beneficiaries vary by the sponsor's duty status and geographic location. This report answers selected frequently asked questions about military health care, including How is the Military Health System structured? What is TRICARE? What are the different TRICARE plans and who is eligible? What are the costs of military health care to beneficiaries? What is the relationship of TRICARE to Medicare? How does the Affordable Care Act affect TRICARE? When can beneficiaries change their TRICARE plan? What is the Medicare Eligible Retiree Health Care fund, which funds TRICARE for Life? This report does not address issues specific to battlefield medicine, veterans, or the Veterans Health Administration.