Given that states have long considered elections a purely domestic matter, the dramatic growth of international election monitoring in the 1990s was remarkable. Why did states allow international organizations and nongovernmental organizations (NGOs) to interfere and why did international election monitoring spread so quickly? Why did election monitoring become institutionalized in so many organizations? Perhaps most puzzling, why do countries invite monitors and nevertheless cheat? This article develops a rigorous method for investigating the causal mechanisms underlying the rise of election monitoring, and “norm cascades” more generally. The evolution and spread of norms, as with many other social processes, are complex combinations of normative, instrumental, and other constraints and causes of action. The rise of election monitoring has been driven by an interaction of instrumentalism, emergent norms, and fundamental power shifts in the international system. By dissecting this larger theoretical complexity into specific subclaims that can be empirically investigated, this article examines the role of each of these causal factors, their mutual tensions, and their interactive contributions to the evolution of election monitoring.Versions of this article were presented at annual meetings of the International Studies Association and the American Political Science Association, and at a conference at Northwestern University. I thank Michael Barnett, Valarie Bunce, Jeff Checkel, Gary Goertz, Ian Hurd, Bruce Jentleson, Peter Katzenstein, Fritz Mayer, Layna Mosley, Arturo Santa-Cruz, and three anonymous reviewers for comments on earlier drafts. I am grateful to Lenka Siroki and Valentino Nikolova for research assistance. This material is based on work supported by the National Science Foundation under Grant No. 0550111. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.