How it works
A Health insurance policy is a contract between an insurance company and an individual. The contract can be renewable annually or monthly. The type and amount of health care costs that will be covered by the health plan are specified in advance, in the member contract or Evidence of Coverage booklet. The individual policy-holder's payment obligations may take several forms:

Premium: The amount the policy-holder pays to the health plan each month to purchase health coverage.
Deductible: The amount that the policy-holder must pay out-of-pocket before the health plan pays its share. For example, a policy-holder might have to pay a $500 deductible per year, before any of their health care is covered by the health plan. It may take several doctor's visits or prescription refills before the policy-holder reaches the deductible and the health plan starts to pay for care.
Copayment: The amount that the policy-holder must pay out of pocket before the health plan pays for a particular visit or service. For example, a policy-holder might pay a $45 copayment for a doctor's visit, or to obtain a prescription. A copayment must be paid each time a particular service is obtained.
Coinsurance: Instead of paying a fixed amount up front (a copayment), the policy-holder must pay a percentage of the total cost. For example, the member might have to pay 20% of the cost of a surgery, while the health plan pays the other 80%. Because there is no upper limit on coinsurance, the policy-holder can end up owing very little, or a significant amount, depending on the actual costs of the services they obtain.
Exclusions: Not all services are covered. The policy-holder is generally expected to pay the full cost of non-covered services out of their own pocket.

Coverage limits:
Some health plans only pay for health care up to a certain dollar amount. The policy-holder may be expected to pay any charges in excess of the health plan's maximum payment for a specific service. In addition, some plans have annual or lifetime coverage maximums. In these cases, the health plan will stop payment when they reach the benefit maximum, and the policy-holder must pay all remaining costs.
Out-of-pocket maximums: Similar to coverage limits, except that in this case, the member's payment obligation ends when they reach the out-of-pocket maximum, and the health plan pays all further covered costs. Out-of-pocket maximums can be limited to a specific benefit category (such as prescription drugs) or can apply to all coverage provided during a specific benefit year.

Health plan vs. health insurance
Historically, HMOs tended to use the term "health plan", while commercial insurance companies used the term "health insurance". A health plan can also refer to a subscription-based medical care arrangement offered through health maintenance organization,HMO, PPO, or POS plan. These plans are similar to pre-paid dental, pre-paid legal, and pre-paid vision plans. Pre-paid health plans typically pay for a fixed number of services (for instance, $300 in preventive care, a certain number of days of hospice care or care in a skilled nursing facility, a fixed number of home health visits, a fixed number of spinal manipulation charges, etc.) The services offered are usually at the discretion of a utilization review nurse who is often contracted through the managed care entity providing the subscription health plan. This determination may be made either prior to or after hospital admission (concurrent utilization review).

Inherent problems with insurance
Insurance systems must typically deal with two inherent challenges: adverse selection, which affects any voluntary system, and ex-post moral hazard, which affects any insurance system in which a third party bears major responsibility for payment, whether that is an employer or the government. Some national systems with compulsory insurance utilize systems such as risk equalization and community rating to overcome these inherent problems.

Adverse selection
Insurance companies use the term "adverse selection" to describe the tendency for only those who will benefit from insurance to buy it. Specifically when talking about health insurance, unhealthy people are more likely to purchase health insurance because they anticipate large medical bills. On the other side, people who consider themselves to be reasonably healthy may decide that medical insurance is an unnecessary expense; if they see the doctor once a year and it costs $250, that's much better than making monthly insurance payments of $40. (example figures).
The fundamental concept of insurance is that it balances costs across a large, random sample of individuals. For instance, an insurance company has a pool of 1000 randomly selected subscribers, each paying $100 per month. One person becomes very ill while the others stay healthy, allowing the insurance company to use the money paid by the healthy people to pay for the treatment costs of the sick person. However, when the pool is self-selecting rather than random, as is the case with individuals seeking to purchase health insurance directly, adverse selection is a greater concern. A disproportionate share of health care spending is attributable to individuals with high health care costs. In the US the 1% of the population with the highest spending accounted for 27% of aggregate health care spending in 1996. The highest-spending 5% of the population accounted for more than half of all spending. These patterns were stable through the 1970s and 1980s, and some data suggest that they may have been typical of the mid-to-early 20th century as well. A few individuals have extremely high medical expenses, in extreme cases totaling a half million dollars or more. Adverse selection could leave an insurance company with primarily sick subscribers and no way to balance out the cost of their medical expenses with a large number of healthy subscribers.

Because of adverse selection, insurance companies employ medical underwriting, using a patient's medical history to screen out those whose pre-existing medical conditions pose too great a risk for the risk pool. Before buying health insurance, a person typically fills out a comprehensive medical history form that asks whether the person smokes, how much the person weighs, whether the person has been treated for any of a long list of diseases and so on. In general, those who present large financial burdens are denied coverage or charged high premiums to compensate. One large US industry survey found that roughly 13 percent of applicants for comprehensive, individually purchased health insurance who went through the medical underwriting in 2004 were denied coverage. Declination rates increased significantly with age, rising from 5 percent for individuals 18 and under to just under a third for individuals aged 60 to 64. Among those who were offered coverage, the study found that 76% received offers at standard premium rates, and 22% were offered higher rates. On the other side, applicants can get discounts if they do not smoke and are healthy.

Moral hazard
Moral hazard occurs when an insurer and a consumer enter into a contract under symmetric information, but one party takes action, not taken into account in the contract, which changes the value of the insurance. A common example of moral hazard is third-party payment—when the parties involved in making a decision are not responsible for bearing costs arising from the decision. An example is where doctors and insured patients agree to extra tests which may or may not be necessary. Doctors benefit by avoiding possible malpractice suits, and patients benefit by gaining increased certainty of their medical condition. The cost of these extra tests is borne by the insurance company, which may have had little say in the decision. Co-payments, deductibles, and less generous insurance for services with more elastic demand attempt to combat moral hazard, as they hold the consumer responsible.

Other factors affecting insurance prices
A recent study by PriceWaterhouseCoopers examining the drivers of rising health care costs in the US pointed to increased utilization created by increased consumer demand, new treatments, and more intensive diagnostic testing, as the most significant driver. People in developed countries are living longer. The population of those countries is aging, and a larger group of senior citizens requires more intensive medical care than a young healthier population. Advances in medicine and medical technology can also increase the cost of medical treatment. Lifestyle-related factors can increase utilization and therefore insurance prices, such as: increases in obesity caused by insufficient exercise and unhealthy food choices; excessive alcohol use, smoking, and use of street drugs. Other factors noted by the PWC study included the movement to broader-access plans, higher-priced technologies, and cost-shifting from Medicaid and the uninsured to private payers.

Health insurance in Australia
The public health system is called Medicare. It ensures free universal access to hospital treatment and subsidised out-of-hospital medical treatment. It is funded by a 1.5% tax levy.
The private health system is funded by a number of private health insurance organisations. The largest of these is Medibank Private, which is government-owned, but operates as a government business enterprise under the same regulatory regime as all other registered private health funds. The Coalition Howard government had announced that Medibank would be privatised if it won the 2007 election, however they were defeated by the Australian Labor Party under Kevin Rudd which had already pledged that it would remain in government ownership.
Some private health insurers are 'for profit' enterprises, and some are non-profit organizations such as HCF Health Insurance. Some have membership restricted to particular groups, but the majority have open membership.
Most aspects of private health insurance in Australia are regulated by the Private Health Insurance Act 2007.
The private health system in Australia operates on a "community rating" basis, whereby premiums do not vary solely because of a person's previous medical history, current state of health, or (generally speaking) their age (but see Lifetime Health Cover below). Balancing this are waiting periods, in particular for pre-existing conditions (usually referred to within the industry as PEA, which stands for "pre-existing ailment"). Funds are entitled to impose a waiting period of up to 12 months on benefits for any medical condition the signs and symptoms of which existed during the six months ending on the day the person first took out insurance. They are also entitled to impose a 12-month waiting period for benefits for treatment relating to an obstetric condition, and a 2-month waiting period for all other benefits when a person first takes out private insurance. Funds have the discretion to reduce or remove such waiting periods in individual cases. They are also free not to impose them to begin with, but this would place such a fund at risk of "adverse selection", attracting a disproportionate number of members from other funds, or from the pool of intending members who might otherwise have joined other funds. It would also attract people with existing medical conditions, who might not otherwise have taken out insurance at all because of the denial of benefits for 12 months due to the PEA Rule. The benefits paid out for these conditions would create pressure on premiums for all the fund's members, causing some to drop their membership, which would lead to further rises, and a vicious cycle would ensue.
There are a number of other matters about which funds are not permitted to discriminate between members in terms of premiums, benefits or membership - these include racial origin, religion, sex, sexual orientation, nature of employment, and leisure activities. Premiums for a fund's product that is sold in more than one state can vary from state to state, but not within the same state.

The Australian government has introduced a number of incentives to encourage adults to take out private hospital insurance. These include:
Lifetime Health Cover: If a person has not taken out private hospital cover by the 1st July after their 30th birthday, then when (and if) they do so after this time, their premiums must include a loading of 2% per annum. Thus, a person taking out private cover for the first time at age 40 will pay a 20 per cent loading. The loading continues for 10 years. The loading applies only to premiums for hospital cover, not to ancillary (extras) cover.
Medicare Levy Surcharge: People whose taxable income is greater than a specified amount (currently $50,000 for singles and $100,000 for families) and who do not have an adequate level of private hospital cover must pay a 1% surcharge on top of the standard 1.5% Medicare Levy. The rationale is that if the people in this income group are forced to pay more money one way or another, most would choose to purchase hospital insurance with it, with the possibility of a benefit in the event that they need private hospital treatment - rather than pay it in the form of extra tax as well as having to meet their own private hospital costs.
Private Health Insurance Rebate: The government subsidises the premiums for all private health insurance cover, including hospital and ancillary (extras), by 30%, 35% or 40%.

Health insurance in Canada
Most health insurance in Canada is administered by each province, under the Canada Health Act, which requires all people to have free access to basic health services. Collectively, the public provincial health insurance systems in Canada are frequently referred to as Medicare. Private health insurance is allowed, but the provincial governments allow it only for services that the public health plans do not cover; for example, semi-private or private rooms in hospitals and prescription drug plans. Canadians are free to use private insurance for elective medical services such as laser vision correction surgery, cosmetic surgery, and other non-basic medical procedures. Some 65% of Canadians have some form of supplementary private health insurance; many of them receive it through their employers. Private-sector services not paid for by the government account for nearly 30 percent of total health care spending.
In 2005, the Supreme Court of Quebec ruled, in Chaoulli v. Quebec, that the province's prohibition on private insurance for health care already insured by the provincial plan could constitute an infringement of the right to life and security if there were long wait times for treatment as happened in this case. Certain other provinces have legislation which financially discourages but does not forbid private health insurance in areas covered by the public plans. The ruling has not changed the overall pattern of health insurance across Canada but has spurred on attempts to tackle the core issues of supply and demand and the impact of wait times.

Health insurance in The Netherlands
In the Netherlands in 2006, a new system of health insurance came into force. All insurance companies have to provide at least one policy which meets a government set minimum standard level of cover and all adult residents are obliged by law to purchase this cover from an insurance company of their choice.
The new system avoids the two pitfalls of adverse selection and moral hazard associated with traditional forms of health insurance.
In the Dutch system, insurance companies are compensated for taking on high risk individuals because they receive extra funding for them. This funding comes from an insurance equalization pool run by a regulator which collects salary based contributions from employers (about 45% of all health care funding) and funding from the government for people whose means are such that they cannot afford health care (about 5% of all funding). Thus insurance companies find that insuring high risk individuals becomes an attractive proposition. All insurance companies receive from the pool, but those with more high risk individuals will receive more from the fund. The remaining 45% of health care funding comes from insurance premiums paid by the public. Insurance companies compete for this money on price alone. The insurance companies are not allowed to set down any co-payments or caps or deductibles. Neither are they allowed to deny coverage to any person applying for a policy or charge anything other than their nationally set and internet published standard policy premiums. Every person buying insurance from that company will pay the same price as everyone else buying that policy. And every person will get the minimum level of coverage. Children under 18 are insured for free (the funding coming from the equalization pool).
In addition to this minimum level, companies are free to sell extra insurance for additional coverage over the national minimum, but extra risks for this are not covered from the insurance pool and must therefore be priced accordingly.

Health insurance in the United Kingdom
Great Britain's National Health Service (NHS) is a publicly funded healthcare system that provides coverage to everyone normally resident in the UK. The NHS provides the majority of health care in England, including primary care, in-patient care, long-term health care, ophthalmology and dentistry. Private health care has continued parallel to the NHS, paid for largely by private insurance, but it is used by less than 8% of the population, and generally as a top-up to NHS services. Recently the private sector has been increasingly used to increase NHS capacity despite a large proportion of the British public opposing such involvement.[20]. According to the World Health Organization, government funding covered 86% of overall health care expenditures in the UK as of 2004, with private expenditures covering the remaining 14%.[21] The costs of running the NHS (est. £104 billion in 2007-8)[22] are met directly from general taxation.

The National Health Service Act 1946 came into effect on 5 July 1948. The UK government department responsible for the NHS is the Department of Health, headed by a Secretary of State for Health (Health Secretary), who sits in the British Cabinet. The NHS is the world's largest health service, and the world's third largest employer after the Chinese army and the Indian railways.

Health insurance in the United States
The US market-based health care system relies heavily on private and not-for-profit health insurance, which is the primary source of coverage for most Americans. According to the United States Census Bureau, approximately 84% of Americans have health insurance; some 60% obtain it through an employer, while about 9% purchase it directly. Various government agencies provide coverage to about 27% of Americans (there is some overlap in these figures).
Public programs provide the primary source of coverage for most seniors 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, 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, and SCHIP, also 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.
In 2006, there were 47 million people in the United States (16% of the population) who were without health insurance for at least part of that year. About 37% of the uninsured live in households with an income over $50,000.
In 2004, US health insurers directly employed almost 470,000 people at an average salary of $61,409. (As of the fourth quarter of 2007, the total US labor force stood at 153.6 million, of whom 146.3 million were employed. Employment related to all forms of insurance totaled 2.3 million. Mean annual earnings for full-time civilian workers in June of 2006 were $41,231; median earnings were $33,634.)