I am grateful for the remarkable community of friends and colleagues who have informed me, engaged me, supported me, critiqued me, and loved me in the years this book has been under way. My thanks first to Dan Danielsen for hundreds of breakfast and dinner conversations about every nook and cranny of my argument and more than twenty-five years of intellectual and personal partnership. Had I not met Duncan Kennedy in 1977, I would not have gotten—or kept—a job thinking about law. For almost forty years, we’ve pursued parallel and collaborative play in all kinds of projects: co-teaching, co-organizing, reading one another’s drafts, and strategizing one another’s lives. My ideas about law and everything else in this book have been generated through that collaboration. Many have been enormously generous in reading portions of the manuscript and indulging me in endless conversation about how expertise works, what law is all about, and how the world fits together: particular thanks are due to Guenther Frankenberg, Janet Halley, Sheila Jasanoff, Martti Koskenneimi, Zina Miller, and David Trubek.