In October 2012, the Center for Medicare & Medicaid Innovation 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. To help participating practices achieve these functions, CPC offers three main supports: enhanced payment, data feedback, and learning activities and technical assistance. The substantial transformation involved in executing these functions is expected to achieve better health care, better health outcomes, and lower costs. This is the appendix to the second annual report to CMS that describes the implementation and impacts of CPC over its first two years.