Abdulrahman M. El-Sayed, MD, DPhil, is a public health physician and epidemiologist. He serves the City of Detroit as the Executive Director of the Detroit Health Department and Health Officer. Under his leadership, the Detroit Health Department has emerged as a state and national leader in promoting healthy air quality, lead elimination, and public health innovation. Dr. El-Sayed's research explores urban health policy, the social determinants of health, and health inequalities. Previously, he was a professor in the Department of Epidemiology at Columbia University. Sandro Galea, MD, DrPH, is a physician and an epidemiologist interested in the social production of health of urban populations. His work explores innovative cells-to-society approaches to population health questions. He is interested in advancing a consequentialist approach to population health scholarship. He currently serves as Robert A. Knox Professor and Dean of the School of Public Health at Boston University. He is a past president of the Society for Epidemiologic Research, and an elected member of the National Academy of Medicine. Together they have been engaged in systems science scholarship and education for more than 15 years.