The Mechanisms of Policy Diffusion Charles R. Shipan * Department of Political Science University of Michigan Craig Volden Department of Political Science The Ohio State University Forthcoming, American Journal of Political Science May 8, 2008 Abstract Local policy adoptions provide an excellent opportunity to test among potential mechanisms of policy diffusion. By examining three types of antismoking policy choices by the 675 largest U.S. cities between 1975 and 2000, we uncover robust patterns of policy diffusion, yielding three key findings. First, we distinguish among and find evidence for four mechanisms of policy diffusion: learning from earlier adopters, economic competition among proximate cities, imitation of larger cities, and coercion by state governments. Second, we find a temporal component to these effects, with imitation being a more short-lived diffusion process than the others. Third, we show that these mechanisms are conditional, with larger cities being better able to learn from others, less fearful of economic spillovers, and less likely to rely on imitation. * The authors would like to thank Jacob Nelson, Ken Moffett, Tracy Finlayson, and Chad Diefenderfer for valuable research assistance; Ted Brader, Fred Boehmke, Rob Franzese, and Kurt Weyland for useful discussions and suggestions; and seminar participants at University of Arizona, Florida State University, Keio University, University of Illinois, University of Michigan, New York University, The Ohio State University, Pennsylvania State University, Stanford University, and the Midwest Political Science Association meetings for helpful comments. We also thank the Robert Wood Johnson Foundation for financial support, and Jamie Chriqui for providing us with the updated version of the National Cancer Institute’s State Cancer Legislative Database. Local tobacco control ordinance data was provided by the American Nonsmokers’ Rights Foundation Local Tobacco Control Ordinance Database © and data on city level demographics was obtained from the Taubman Center for State and Local Government.