As Medicare approaches its 60th anniversary, it almost goes without saying that the program is both popular and successful. Medicare provides health insurance coverage to 67 million older adults and people with disabilities. Medicare is viewed favorably by Democrats, Republicans, and Independents. Medicare has also helped to extend life expectancy and, in conjunction with the Civil Rights Act of 1964, narrow disparities in care. It is a vital source of revenue for hospitals, physicians and other health care providers, and health insurers and is an essential component of health and retirement security in the U.S. These are among the reasons why Medicare is often considered a third rail in politics. Medicare also faces challenges stemming from the growing role of private plans, demographic shifts, and rising health care costs. This paper examines these challenges by focusing on three fundamental questions. First, what are the implications of the transformation that is taking place with private insurers playing a more dominant role in providing Medicare benefits? Second, what changes may be important to address the gaps in covered benefits and related affordability challenges? Third, how can Medicare be sustained to finance care for current and future generations?