Medicare Advantage plans are an alternative to Medicare Parts A and B. A Medicare Advantage plan (called Part C) is offered by a private insurer or HMO and offers its enrollees the same Medicare-eligible health care services available to beneficiaries under Parts A and B. The federal government pays the insurer a set amount for each enrollee. In addition, Medicare Advantage plan enrollees usually get additional coverage not offered by Parts A and B. In most, but not all, Medicare Advantage plans, there is a monthly premium in addition to what you would pay for Medicare Parts A and B.