The Medicare Prescription Drug, Improvement, and Modernization Act of 2003 established a voluntary, outpatient prescription drug benefit under Medicare Part D, effective January 1, 2006. Medicare Part D provides coverage through private prescription drug plans (PDPs) that offer only drug coverage, or through Medicare Advantage (MA) prescription drug plans (MA-PDs) that offer coverage as part of broader, managed care plans. Private drug plans participating in Part D bear some financial risk, though federal subsidies cover most program costs in an effort to encourage participation and keep benefits affordable. This book discusses the prescription drug benefit of Medicare Part D. It also examines practices for promoting prescription drug program integrity, and the extent that CMS's oversight of Medicare Part D program integrity, including the program integrity contractors, reflects these practices.