PPO: Preferred Provider Organization. A PPO allows you the freedom to choose your own doctors and facilities. Even if the doctor or facility is not in-network, the insurance is still responsible for their portion. A PPO also allows you to go straight to a specialist without requiring a referral from a Primary Care Physician. HMO: Health Maintenance Organization. A HMO may only give access to a limited number of doctors and facilities in its small network. If one seeks care out-of-network then the insurance company may not be responsible for any of the bill unless deemed a life-threatening emergency. A HMO typically requires you to have a referral from your Primary Care Physician before being able to see a specialist.