In FY 2016, the Medicare program will cover approximately 57 million beneficiaries (48 million aged and 9 million disabled) at a total cost of about $701 billion. Spending under the program (except for a portion of administrative costs) is considered mandatory spending and is not subject to the appropriations process. Since its inception, it has undergone many changes. A new report from the Congressional Research Service (CRS) provides a general overview of the program, including descriptions of its history, eligibility criteria, covered services, provider payment systems, and program administration and financing. 

The report can be accessed at http://fas.org/sgp/crs/misc/R40425.pdf.