In October 2012, the Center for Medicare & Medicaid Innovation (CMMI) of the Centers for Medicare & Medicaid Services (CMS) launched the four-year Comprehensive Primary Care (CPC) initiative. The goal of CPC was to improve primary care delivery, health care quality, and patient experience, and lower costs. CPC also aimed to enhance clinicians’ and staff members’ experience. CMS leveraged the support of 39 other public and private payers to target the transformation of primary care delivery in nearly 500 primary care practices in seven regions across the United States. These practices included more than 2,000 clinicians and served around 3 million patients. CPC required practices to transform across five key care delivery functions: (1) access and continuity, (2) planned care for chronic conditions and preventive care, (3) risk-stratified care management, (4) patient and caregiver engagement, and (5) coordination of care across the medical neighborhood. CMS specified a series of Milestones to help move practices along the path of implementing the five functions, and it updated the requirements for each Milestone annually to build on practices’ progress in the prior year. CMS assessed whether practices met targets set within the Milestones, which were considered minimum requirements to remain in the initiative. Although the CPC Milestones overlap with many of the activities typically included in existing patient-centered medical home (PCMH) recognition programs, CPC did not require practices to have or obtain PCMH recognition, although nearly 40 percent did have this recognition when they applied to CPC. CPC supported practices’ transformation with: (1) prospective care management fees and the opportunity to earn shared savings in addition to their usual payments; (2) data feedback on cost, utilization, and quality; and (3) learning support