This project has been in the works for two decades or more, and many people have stimulated my thinking about punishment theory over that time. My greatest intellectual debt is to John Darley, Warren Professor of Psychology at Princeton. He and I have coauthored several articles that make up the foundation for several chapters in this book, in particular Chapter 3 and 8. Many of the ideas contained in those chapters originated with him. I am also indebted to law students in my punishment theory seminars at the University of Pennsylvania Law School, who provided both original ideas and a challenge to me to better develop and express my own. Special thanks go to Scott Kaplan, of the University of Pennsylvania Law School Class of 2009, who provided enormously helpful research assistance in the production of this book. Finally, I repeat my now well-worn thanks for the support of Sarah McAlpine Robinson, my spouse, my love, my best friend.