HMO (Health Maintenance Organization) - Offers healthcare services only with specific HMO providers. Under an HMO plan, you might have to choose a primary care doctor. This doctor will be your main healthcare provider. The doctor will refer you to other HMO specialists when needed. Services from providers outside the HMO plan are hardly ever covered except for emergencies. 

^ Leichter, Howard M. (1979). A comparative approach to policy analysis: health care policy in four nations. Cambridge: Cambridge University Press. p. 121. ISBN 978-0-521-22648-6. The Sickness Insurance Law (1883). Eligibility. The Sickness Insurance Law came into effect in December 1884. It provided for compulsory participation by all industrial wage earners (i.e., manual laborers) in factories, ironworks, mines, shipbuilding yards, and similar workplaces.
Critics said that "Exemptions would lead to market instability and higher premiums in the traditional small-group market. AHPs exempt from state regulation and oversight would enable them to be more selective about who they cover. They will be less likely to cover higher-risk populations, which would cause an imbalance in the risk pool for other small business health plans that are part of the state small group risk pool. Adverse selection would likely abound and Association Health Plans would be selling an unregulated product alongside small group plans, which creates an unlevel playing field."[79] According to the Congressional Budget Office (CBO), "[p]remiums would go up for those buying in the traditional small-group market." competing against AHPs that offer less expensive and less comprehensive plans.[79][82]
Co-payments were introduced in the 1980s in an attempt to prevent over utilization. The average length of hospital stay in Germany has decreased in recent years from 14 days to 9 days, still considerably longer than average stays in the United States (5 to 6 days).[28][29] Part of the difference is that the chief consideration for hospital reimbursement is the number of hospital days as opposed to procedures or diagnosis. Drug costs have increased substantially, rising nearly 60% from 1991 through 2005. Despite attempts to contain costs, overall health care expenditures rose to 10.7% of GDP in 2005, comparable to other western European nations, but substantially less than that spent in the U.S. (nearly 16% of GDP).[30]
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.
When small group plans are medically underwritten, employees are asked to provide health information about themselves and their covered family members when they apply for coverage. When determining rates, insurance companies use the medical information on these applications. Sometimes they will request additional information from an applicant's physician or ask the applicants for clarification.[73]
Public insurance cover increased from 2000–2010 in part because of an aging population and an economic downturn in the latter part of the decade. Funding for Medicaid and CHIP expanded significantly under the 2010 health reform bill.[9] The proportion of individuals covered by Medicaid increased from 10.5% in 2000 to 14.5% in 2010 and 20% in 2015. The proportion covered by Medicare increased from 13.5% in 2000 to 15.9% in 2010, then decreased to 14% in 2015.[3][10]