We are adding to our regulations a new part to contain rules that we will apply when we evaluate applications for premium and cost- sharing subsidies under the Medicare program. We are including a new subpart, Medicare Part D Subsidies, to this part. This new subpart contains the rules that we use to determine eligibility for premium and cost-sharing subsidies under the Medicare Part D program, which was added by the Medicare Prescription Drug, Improvement, and Modernization Act of 2003 (Medicare Modernization Act or MMA). These final rules describe: What the new subpart is about; how we determine whether you are eligible for premium and cost-sharing subsidies; how we redetermine your eligibility for a subsidy; how you apply for a subsidy; how we evaluate your income and resources; when your eligibility for premium and cost-sharing subsidies terminates; how you may report changes in your circumstances; and how you can appeal a determination we make under the Part D subsidy program.