In the course of this project, I have benefi ted from the wisdom and kindness of many wonderful people. Peter Hall’s research on the infl uence of ideas inspired me to start this project, and his generosity in advising and commenting on many versions of the project kept me going. Torben Iversen’s undergraduate seminars showed me that great research could be done in the fi eld of social policy; I have profi ted from his insights and his support for more than a decade. Beth Simmons’ work on compliance and diff usion critically shaped my thinking. Th is project draws heavily from her work, and her detailed comments on many draft s have pushed it much further than it would have otherwise gone. Ryan Goodman’s research on socializing states inspired me to think carefully about how to connect diff usion research to debates about the design of international institutions. He has combed through multiple draft s over many years, with very helpful suggestions each time. Jack Goldsmith has been an amazing mentor, and helped me to develop provocative ideas, even when he disagreed with them. Martha Minow and Amartya Sen cheered me on in my three years at the Society of Fellows, and provided much guidance over delicious meals.