HMOs often require members to select a [[primary care physician]] (PCP), a doctor who acts as a [[gatekeeper]] to direct access to medical services but this is not always the case. PCPs are usually [[internist]]s, [[pediatrician]]s, [[family doctor]]s, [[geriatrician]]s, or [[general practitioner]]s (GPs). Except in medical emergency situations, patients need a referral from the PCP in order to see a specialist or other doctor, and the gatekeeper cannot authorize that referral unless the HMO guidelines deem it necessary. Some HMOs pay gatekeeper PCPs set fees for each defined medical procedure they provide to insured patients ([[fee-for-service]]) and then [[Capitation (healthcare)|capitate]] specialists (that is, pay a set fee for each insured person’s care, irrespective of which medical procedures the specialists performs to achieve that care), while others use the reverse arrangement.

Open-access and point-of-service (POS) products are a combination of an HMO and traditional indemnity plan. The member(s) are not required to use a gatekeeper or obtain a referral before seeing a specialist. In that case, the traditional benefits are applicable. If the member uses a gatekeeper, the HMO benefits are applied. However, the beneficiary cost sharing (e.g., co-payment or coinsurance) may be higher for specialist care.{{cite book|first=Peter R.|last=Kongstvedt|title=The Managed Health Care Handbook|edition=Fourth|publisher=Aspen Publishers|date=2001|page=40|isbn=0-8342-1726-0}} HMOs also manage care through utilization review. That means they monitor doctors to see if they are performing more services for their patients than other doctors, or fewer. HMOs often provide [[preventive care]] for a lower [[copayment]] or for free, in order to keep members from developing a preventable condition that would require a great deal of medical services. When HMOs were coming into existence, indemnity plans often did not cover preventive services, such as [[immunizations]], [[Well-baby visit|well-baby checkups]], [[mammograms]], or physicals. It is this inclusion of services intended to maintain a member’s health that gave the HMO its name. Some services, such as [[outpatient]] mental health care, are limited, and more costly forms of care, diagnosis, or treatment may not be covered. Experimental treatments and elective services that are not medically necessary (such as elective [[plastic surgery]]) are almost never covered.

Other choices for managing care are [[Case management (USA health system)|case management]], in which patients with catastrophic cases are identified, or [[Disease management (health)|disease management]], in which patients with certain chronic diseases like [[diabetes]], [[asthma]], or some forms of [[cancer]] are identified. In either case, the HMO takes a greater level of involvement in the patient’s care, assigning a case manager to the patient or a group of patients to ensure that no two providers provide overlapping care, and to ensure that the patient is receiving appropriate treatment, so that the condition does not worsen beyond what can be helped.
wikipedia