Health maintenance organisations represent "pre-paid" or "capitated" insurance plans in which individuals or their employers pay a fixed monthly fee for services instead of a separate charge for each visit or service. The monthly fees remain the same, regardless of types or levels of services provided. Services are provided by physicians who are employed by, or under contract with, the HMO. HMOs vary in design. Depending on the type of the HMO, services may be provided in a central facility, or in a physician's own office (as with IPAs.)