HMOs offer prepaid, comprehensive health coverage for both hospital and physician services. The HMO is paid monthly premiums or capitated rates by the payers, which include employers, insurance companies, government agencies, and other groups representing covered lives. The HMO must meet the specifications of the federal HMO act as well as meeting many rules and regulations required at the state level. There are 4 basic models: group model, individual practice association, network model and staff model. An HMO contracts with health care providers, e.g., physicians, hospitals, and other health professionals. The members of an HMO are required to use participating or approved providers for all health services and generally all services will need to meet further approval by the HMO through its utilization program. Members are enrolled for a specified period of time. HMOs may turn around and sub-capitate to other groups. For example, it may carve-out certain benefit categories, such as mental health, and subcapitate these to a mental health HMO. Or the HMO may subcapitate to a provider, provider group or provider network. HMOs are the most restrictive form of managed care benefit plans because they restrict the procedures, providers and benefits.