This issue of Primary Care: Clinics in Office Practice, guest edited by Drs. Anthony J. Viera and Devdutta Sangvai, is devoted to Population Health. Articles in this issue include: What is Population Health?; Measuring Health; Prevention as a Population Health Strategy; Value-Based Care; The Business Case for Population Health Management; Primary Care Transformation; Patient Engagement; Quality Improvement Principles and Practice; Lean Management; Population Health and AMCs: High cost meets high efficiency; Models of Population Health Management; Tools for Population Health Management; Clinically Integrated Networks; Assessing and Addressing Social Determinants of Health; and Population Health Policies.