The Federal Employees Health Benefits Program (FEHBP) has been in existence for over 50 years. Since its creation, it has provided private health insurance coverage to federal employees, annuitants, and their dependents. It is the largest employer-sponsored health insurance program in the country; in 2010, nearly 8 million individuals were covered under FEHBP. The program was created by the Federal Employees Health Benefits Act of 1959 (FEHBA, P.L. 86-382). FEHBA and its subsequent amendments established the parameters for eligibility and the election of coverage; the types of health plans and benefits that may be offered; the level of the government's share of premiums; the Employees Health Benefits Fund to pay for program expenses; and provisions for studies, reports, and audits. FEHBA also outlined the role of the Office of Personnel Management (OPM). By law, OPM is given the authority to contract with insurers and to prescribe regulations to manage FEHBP, among other duties. The general model of FEHBP has not changed since its inception in 1959. FEHBP was and is a program that allows competing private insurers to offer numerous types of coverage to enrollees within broad federal guidelines. The federal government and the employee/annuitant have always shared the cost of the premium, and generally, employees and annuitants have always had access to the same plans at the same cost. However, specific features of FEHBP have been modified, in some cases multiple times, by Congress and OPM. For example, eligibility has been expanded to include additional types of federal employees and dependents, the formula for determining the government's share of premiums has changed, and the types of health benefits offered through FEHBP plans have been broadened. Congressional policymakers share responsibility with OPM for the program's viability and sustainability. Congress has financial and administrative interest in the program, as the government pays for a share of FEHBP premiums and Congress has legislative authority to modify FEHBP. Congressional interest in FEHBP also extends to FEHBP's potential applicability as a model for other health care programs or as an avenue to provide coverage, such as extending aspects of FEHBP to Medicare, or using it as one of the models for the state exchanges under the Patient Protection and Affordable Care Act (ACA, P.L. 111-148, as amended). The purpose of the report is to provide historical and background information that helps explain how FEHBP has evolved into the program it is today. Policymakers may use this report to understand how Congress has interacted with FEHBP in the past, and to inform its future interactions with FEHBP. Specifically, the report includes short discussions of how Congress has effected and maintained policy changes to FEHBP by restricting the use of federal funds; changed the formula for determining the government's share of FEHBP premiums; expanded eligibility for the program; and implemented policies that affect the relationship between Medicare and FEHBP.