This report provides an overview of Medicare Part B premiums, including information on Part B eligibility and enrollment, late-enrollment penalties, collection of premiums, determination of annual premium amounts, premiums for high-income enrollees, premium assistance for low-income enrollees, protections for Social Security recipients from rising Part B premiums, and historical Medicare Part B premium trends. This report also provides a summary of various premium-related issues that may be of interest to Congress. Specific Medicare and Social Security publications and other resources for beneficiaries, and those who provide assistance to them, are cited where appropriate.