Two distinct views of the roles and responsibilities of epidemiologists have emerged in a decades-long debate: one keeps professional practice constrained to science; the other adds active participation in public health policymaking. In defense of the narrower view are several claims: that epidemiologists lack expertise in policymaking; that advocating policy adversely affects scientific objectivity; that the limits of epidemiologic science work against translating results into policy; and that participation in policy can bring on personal attacks. In this study, each claim is addressed. Epidemiologists already participate fully in educational, research funding, and editorial policymaking and thereby have an experiential foundation in some of the basics of policymaking. Policymaking can enhance scientific objectivity because it requires not only the use but more importantly the improvement of empirical methods. Finally, the comforts of professional life are not the primary yardsticks of our responsibilities. Arguments in favor of active involvement in public health policymaking are presented. Epidemiologists have been mixing science and policymaking for a long time and there is a strong sense that the benefits of public stewardship outweigh the risks. The American College of Epidemiology's Ethics Guidelines support this view. Active participation in public heath policymaking will, however, require curriculum changes in graduate training programs. With additional training and a broader recognition that public health policymaking is an appropriate professional pursuit, epidemiologists can look to a bright and challenging future in the science and practice of public health.