Tricare (styled TRICARE) is a health care program of the United States Department of Defense Military Health System. Tricare provides civilian health benefits for U.S Armed Forces military personnel, military retirees, and their dependents, including some members of the reserve component. Tricare is the civilian care component of the Military Health System, although historically it also included health care delivered in military medical treatment facilities.

The Tricare program is managed by the Defense Health Agency. Before 1 October 2013, it was managed by the Tricare Management Activity under the authority of the assistant secretary of defense (health affairs). On that date, it was disestablished and Tricare responsibility was transferred to the newly established Defense Health Agency.

The Department of Defense operates a health care delivery system that served approximately 9.4 million beneficiaries in 2018. The Department of Defense's unified medical program represents $50.6 billion or 8% of total FY2019 U.S. military spending. With the exception of active duty service members (who are assigned to the Tricare Prime option and pay no out-of-pocket costs for Tricare coverage), Military Health System beneficiaries may have a choice of Tricare plan options depending upon their status (e.g., active duty family member, retiree, reservist, child under age 26 ineligible for family coverage, Medicare-eligible, etc.) and geographic location.

Historically, health care for military personnel and their dependents was provided in military medical facilities as promised by the military, and through a referral system by civilian medical personnel where military physicians were not available in a certain specialty, or when and where overcrowding of a military medical facility occurred.

Active duty military personnel always have priority for care in military medical facilities. After World War II and the Korean War, especially with the growth in the standing forces of the U.S. military due to the Cold War, access to care in military facilities became increasingly unavailable for military retirees and the dependents of both active duty and retired military personnel due to resource constraints and growing demands on the system. It was at this time that the concept of "space-available basis" for military retirees and military dependents was first noted. To address this problem, Congress passed the Dependents Medical Care Act of 1956 and the Military Medical Benefits Amendments of 1966. These acts allowed the Secretary of Defense to contract with civilian health care providers. This civilian health care program became known as the Civilian Health and Medical Program of the Uniformed Services (CHAMPUS) in 1966.

In the late 1980s, because of escalating costs, paperwork demands, and general beneficiary dissatisfaction, DoD initiated a series of demonstration projects. Under a program known as the CHAMPUS Reform Initiative, a contractor provided both health care and administrative-related services, including claims processing. The Tricare Reserve Retired project was one of the first to introduce managed care features to the CHAMPUS program. Beneficiaries were offered three choices – a health maintenance organization-like option called Tricare (CHAMPUS) Prime that required enrollment and offered enhanced benefits and low cost sharing, a preferred provider organization-like option called Tricare (CHAMPUS) Extra that required use of network providers in exchange for lower cost sharing, and the standard CHAMPUS option that continued the freedom of choice in selecting providers but required higher cost sharing and insurance deductibles known as Tricare Standard.

Although DOD's initial intent under the CHAMPUS Reform Initiative was to award three competitively bid contracts covering six states, only one bid, made by Foundation Health Corporation (now Health Net) covering California and Hawaii, was received. Foundation delivered services under this contract between August 1988 and January 1994.

In late 1993, in response to requirements in the National Defense Authorization Act for Fiscal Year 1994, the DoD announced plans for implementing a nationwide managed care program for the MHS that would be completely implemented by May 1997. Under this program, known as Tricare, the United States was divided into 12 health care regions. An administrative organization, the lead agent, was designated for each region and coordinated the health care needs of all military treatment facilities in the region. Under Tricare, seven managed care support contracts were awarded covering DOD's 12 health care regions.