Hospital and medical expense policies were introduced during the first half of the 20th century. During the 1920s, individual hospitals began offering services to individuals on a pre-paid basis, eventually leading to the development of Blue Cross organizations. The predecessors of today's Health Maintenance Organizations (HMOs) originated beginning in 1929, through the 1930s and on during World War II.
Carrin, Guy; James, Chris (January 2005). "Social health insurance: Key factors affecting the transition towards universal coverage" (PDF). International Social Security Review. 58 (1): 45–64. doi:10.1111/j.1468-246x.2005.00209.x. Retrieved 10 March 2013. Initially the health insurance law of 1883 covered blue-collar workers in selected industries, craftspeople and other selected professionals.6 It is estimated that this law brought health insurance coverage up from 5 to 10 per cent of the total population.
The United States health care system relies heavily on private health insurance, which is the primary source of coverage for most Americans. As of 2012 about 61% of Americans had private health insurance according to the Centers for Disease Control and Prevention. The Agency for Healthcare Research and Quality (AHRQ) found that in 2011, private insurance was billed for 12.2 million U.S. inpatient hospital stays and incurred approximately $112.5 billion in aggregate inpatient hospital costs (29% of the total national aggregate costs). Public programs provide the primary source of coverage for most senior citizens and for low-income children and families who meet certain eligibility requirements. The primary public programs are Medicare, a federal social insurance program for seniors and certain disabled individuals; and Medicaid, funded jointly by the federal government and states but administered at the state level, which covers certain very low income children and their families. Together, Medicare and Medicaid accounted for approximately 63 percent of the national inpatient hospital costs in 2011. SCHIP is a federal-state partnership that serves certain children and families who do not qualify for Medicaid but who cannot afford private coverage. Other public programs include military health benefits provided through TRICARE and the Veterans Health Administration and benefits provided through the Indian Health Service. Some states have additional programs for low-income individuals.