Observation services fall under the Centers for Medicare and Medicaid Services (CMS). CMS employs a formal rule making process involving proposed rules released in July, followed by a commentary period and the Outpatient Prospective Payment System (OPPS) final rule, which governs observation hospital services, published in the Federal Register in November. Individual Medicare Administrative Contractors (MACs) oversee the implementation of CMS rules and regulations, with each MAC typically covering several states. The United States is also divided into four regional Recovery Audit Contractor (RAC) regions. Medicare itself has subdivisions with Part A Medicare covering inpatient expenses and Part B Medicare addressing outpatient services.