HMO and PPO are the two most common health plan structures, and the difference between them comes down to a tradeoff: lower cost and more structure, versus higher cost and more freedom. * An HMO — Health Maintenance Organization — generally charges lower monthly premiums in exchange for a more restricted network. You choose a primary care doctor who coordinates your care, and if you need to see a specialist, that primary care doctor typically has to refer you first. Step outside the HMO's network for non-emergency care, and the plan usually won't cover it at all. * A PPO — Preferred Provider Organization — costs more each month, but gives you significantly more flexibility. You can see specialists without getting a referral first, and PPO plans typically cover both in-network and out-of-network care, though you'll pay more out of pocket for going outside the network. * The right choice often comes down to how much you value predictability and lower monthly cost versus flexibility to choose your own specialists and providers without extra coordination. People who already have an established relationship with an out-of-network doctor, or who travel frequently and want more provider options, often lean toward PPOs despite the higher premium. * Two other plan types show up alongside HMOs and PPOs less commonly: an EPO (Exclusive Provider Organization) skips the referral requirement but still restricts you to an in-network, and a POS (Point of Service) plan blends HMO-style referrals with some PPO-style out-of-network flexibility.