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.
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.[56] 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).[57] 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.[57] 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.[58]
The Affordable Care Act dramatically expanded Medicaid. The program will now cover everyone with incomes under 133% of the federal poverty level who does not qualify for Medicare, provided this expansion of coverage has been accepted by the state where the person resides. Meanwhile, Medicaid benefits must be the same as the essential benefit in the newly created state exchanges. The federal government will fully fund the expansion of Medicaid initially, with some of the financial responsibility gradually devolving back to the states by 2020.
States regulate small group premium rates, typically by placing limits on the premium variation allowable between groups (rate bands). Insurers price to recover their costs over their entire book of small group business while abiding by state rating rules.[74] Over time, the effect of initial underwriting "wears off" as the cost of a group regresses towards the mean. Recent claim experience—whether better or worse than average—is a strong predictor of future costs in the near term. But the average health status of a particular small employer group tends to regress over time towards that of an average group.[75] The process used to price small group coverage changes when a state enacts small group reform laws.[76]
Finally achieving universal health coverage remained a top priority among Democrats, and passing a health reform bill was one of the Obama Administration's top priorities. The Patient Protection and Affordable Care Act was similar to the Nixon and Clinton plans, mandating coverage, penalizing employers who failed to provide it, and creating mechanisms for people to pool risk and buy insurance collectively.[9] Earlier versions of the bill included a publicly run insurer that could compete to cover those without employer sponsored coverage (the so-called public option), but this was ultimately stripped to secure the support of moderates. The bill passed the Senate in December 2009 with all Democrats voting in favor and the House in March 2010 with the support of most Democrats. Not a single Republican voted in favor of it either time.

In addition to medical expense insurance, "health insurance" may also refer to insurance covering disability or long-term nursing or custodial care needs. Different health insurance provides different levels of financial protection and the scope of coverage can vary widely, with more than 40% of insured individuals reporting that their plans do not adequately meet their needs as of 2007.[2]