In October 2012, the Center for Medicare & Medicaid Innovation (CMMI) of the Centers for Medicare & Medicaid Services (CMS), in a unique collaboration between public and private health care payers, launched the Comprehensive Primary Care (CPC) initiative to improve primary care delivery in seven regions across the United States. CPC requires that practices meet annual Milestones that help them build the capability to deliver CPC’s five functions:(1) access and continuity,(2) planned chronic and preventive care,(3) risk-stratified care management,(4) patient and caregiver engagement, and (5) coordination of care across the medical neighborhood (Figure ES. 1). To help participating practices achieve these functions, CPC offers three main supports: enhanced payment, data feedback, and learning activities and technical assistance (TA). The substantial transformation involved in achieving these functions is expected to achieve better health care, better health outcomes, and lower costs. This first annual report to CMS describes the implementation and impacts of CPC over its first year.