Political scientists, sociologists, and economists have all sought to analyze the spread of economic and political liberalism across countries in recent decades+ This article documents this diffusion of liberal policies and politics and proposes four distinct theories to explain how the prior choices of some countries and international actors affect the subsequent behavior of others: coercion, competition, learning, and emulation+ These theories are explored empirically in the symposium articles that follow+ The goal of the symposium is to bring quite different and often isolated schools of thought into contact and communication with one another, and to define common metrics by which we can judge the utility of the contending approaches to diffusion across different policy domains+The worldwide spread of economic and political liberalism was the defining feature of the late twentieth century+ Free-market-oriented economic reformsmacroeconomic stabilization, liberalization of foreign economic policies, privatization, and deregulation-took root in many parts of the world+ At more or less the same time, a "third wave" of democratization and liberal constitutionalism washed over much of the globe+ Most economists believe the gains to developing countries from the liberalization of economic policies to be in the hundreds of billions of dollars+ But they also acknowledge the instability and human insecurity sometimes left in liberalization's wake+ 1 Political scientists argue that the rise of democracy has contributed to the betterment of both human rights and international security+ 2 While the precise effects of these twin waves of liberalization are still debated, it is hard to deny that they have had a tremendous impact on the For helpful comments on an earlier draft of this article, the authors wish to thank