This document discusses several common payment mechanisms used in the US healthcare system, including Medicaid/Medicare, out-of-pocket expenses, and preferred provider organizations (PPOs). Medicaid/Medicare accounts for a large portion of US healthcare spending and debt. Patients are also responsible for out-of-pocket costs like co-payments that are rising faster than incomes. PPOs allow patients to choose providers both in and out of their insurance network, and these plans are becoming more popular for Medicare recipients. Billing and payment collection are essential to fund the entire healthcare system.