How can public health researchers who study policy change understand the relative roles of evidence and power in improving population health? In a new commentary now online in the American Journal of Public Health, two City University of New York School of Public Health faculty, Dr. Nicholas Freudenberg, distinguished professor of public health, and Dr. Emma Tsui, assistant professor of public health, take on this question. Arguing that meaningful improvements in health require modifying the social determinants of health and that policies are often underlying causes of the living conditions that shape health, Drs. Freudenberg and Tsui make the case that effective action to promote policies that improve population health requires a deeper analysis of the roles of scientific evidence and political power in bringing about policy change. They encourage researchers committed to the use of community-based participatory research to identify the appropriate scales for policy change, from community to global, and the participatory processes that acknowledge the interplay between power and evidence.