Before the development of medical expense insurance, patients were expected to pay all other health care costs out of their own pockets, under what is known as the fee-for-service business model. During the middle to late 20th century, traditional disability insurance evolved into modern health insurance programs. Today, most comprehensive private health insurance programs cover the cost of routine, preventive, and emergency health care procedures, and also most prescription drugs, but this was not always the case. The rise of private insurance was accompanied by the gradual expansion of public insurance programs for those who could not acquire coverage through the market.

On the whole, uninsured Americans have worse health outcomes; cancers and other deadly diseases, for example, are more likely to be diagnosed at later stages in uninsured people. Uninsured pregnant women use fewer prenatal services and uninsured children and adults are less likely than their insured counterparts to have a primary care doctor whom they trust.
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.[65] The predecessors of today's Health Maintenance Organizations (HMOs) originated beginning in 1929, through the 1930s and on during World War II.[67][68]
The employer typically makes a substantial contribution towards the cost of coverage. Typically, employers pay about 85% of the insurance premium for their employees, and about 75% of the premium for their employees' dependents. The employee pays the remaining fraction of the premium, usually with pre-tax/tax-exempt earnings. These percentages have been stable since 1999.[58] Health benefits provided by employers are also tax-favored: Employee contributions can be made on a pre-tax basis if the employer offers the benefits through a section 125 cafeteria plan.
Health insurance in the United States is any program that helps pay for medical expenses, whether through privately purchased insurance, social insurance, or a social welfare program funded by the government.[1] Synonyms for this usage include "health coverage", "health care coverage", and "health benefits". In a more technical sense, the term "health insurance" is used to describe any form of insurance providing protection against the costs of medical services. This usage includes private insurance and social insurance programs such as Medicare, which pools resources and spreads the financial risk associated with major medical expenses across the entire population to protect everyone, as well as social welfare programs like Medicaid and the Children's Health Insurance Program, which both provide assistance to people who cannot afford health coverage.