The ways in which innovations diffuse among jurisdictions and the factors that encourage diffusion have long been a topic of significant interest for scholars of public policy. This large body of work has produced a rich and important set of insights regarding the ways in which policies spread among governments and, particularly, about the manner in which policy makers gather information about innovations and learn from the experiences of previous adopters in that process. Despite these insights, however, there are still significant gaps in our knowledge about the mechanisms of diffusion the degree to which relationships reported in the literature are causal. In part these gaps are an inescapable byproduct of the unique difficulties of studying the diffusion of innovations, but they also arise in part from the research designs that have dominated this field of study. Among other shortcomings, critics have suggested that these designs: have ignored the variation that often characterizes policies within the same issue area, been too focused on adoption versus other stages in the policy process, been relatively under informed by positive theory, and been too quick to replicate accepted, but potentially flawed, methods and measures for studying diffusion. This panel seeks to extend the research on policy diffusion with papers that directly address these challenges. Specifically, the papers: explore the agenda setting stage of the policy process in order to gain better leverage on the causal mechanisms of diffusion; draw on mathematical models of decision making in order to generate more theoretically informed hypotheses about when lawmakers should choose to reject the status quo in favor of policy innovations; examine the surprising variation in “abortion” policies in order to challenge traditional explanations policy making in this highly salient area; and, finally, investigate the utility of measuring information gathering and learning directly rather than inferring these activities indirectly from patterns of policy adoption. Hopefully, these papers and the discussion they motivate will help to both expand and refine our understanding the diffusion of public policies among governments.