Most insurance plans have a network of doctors and hospitals that are "participating" in the network. This means that you are allowed to use these providers and that the plan will pay according to the plan rules. There are caveats and exceptions, of course (and you will find this to be true in nearly every aspect of health care), some of which are explained below. A plan will have two coverage tiers, one for In Network providers and services, and one for Out of Network.
Types of Plans: HMO vs. PPO vs. POS
HMO stands for Health Maintenance Organization and is typically the most restrictive in terms of who you see or what kind of coverage you have; but also can be the most generous in terms of coverage (resulting in low per-use-cost to you.) With an HMO you must select a Primary Care Physician (also known as a PCP). Women are allowed two PCPs; a family doctor or general practitioner, and an OB-GYN. The impact to you: if you want to see any doctor other than your PCP, then a) the doctor must be in the HMO network and b) you must obtain a referral from your PCP. If either condition is not met, your plan pays nothing. Just to be clear on this very important point; if your plan pays nothing, you pay everything regarding that visit and any subsequent health care on the same issue. With an HMO, there is no out of network option.
PPO stands for Preferred Provider Organization and is typically the most flexible in terms of who you see for your care and how often, and typically the most expensive in terms of premiums. PPO’s may require that you select a PCP, but you can see any doctor that is in their network and the plan will pay its in-network rate. In addition, you have the flexibility to go out of network if you wish. The plan will pay less (i.e., you pay more) if you do, but the option is there.
POS stands for Point of Service, and typically falls between the HMO and the PPO in price and flexibility. A PPO does have out of network coverage, and does require a PCP. You are required to obtain a referral from your PCP to see a different doctor.