An IPA, or individual practice association, is a group of doctors that have contracted with an HMO to provide services to the HMO's enrolled subscribers. If you are part of an HMO that has contracted with an IPA in your community, you either pick or have been assigned a primary care physician from a list of doctors participating in an IPA. You would receive your primary care in this doctor's office. This is different from a prepaid practice group.
With a prepaid practice group, the HMO pays salaried staff physicians to provide health care services in HMO-owned facilities.