HMO stands for Health Maintenance Organization and is a type of plan that requires you to see doctors in its network. If you see a doctor outside the network, you will be responsible for all of the costs. The only exception to this is medically necessary emergency or urgent care services. There is also a variation of HMO plans called HMO-POS, which stands for Health Maintenance Organization-Point of Service. These types of plans are similar to HMOs in that you are required to receive most services within the network. However, they have a bit more flexibility and allow you to go out of network for certain services or up to a certain dollar amount. Each plan works differently, so you will need to check to see what is covered out of network for your plan. PPO stands for Preferred Provider Organization and has the most flexibility in allowing you to see doctors out of network. PPO plans have two tiers, an in-network and out of network tier. If you see a doctor in-network, you will typically pay less out-of-pocket for those services. If you see a doctor out-of-network, you will typically have higher out-of-pocket costs, but the services are still covered.