We owe our gratitude to the many people who have contributed invaluably to the development of this book. This includes first and foremost The NASDAQ OMX Educational Foundation, our editor at Columbia University Press, Bridget Flannery-McCoy, Laura Miller, Kevin Haeberle, Menesh Patel, Anne Choike, Yuan Zou, and Polina Dovman. Academically, we owe yet more debts. Thanks to Larry Harris, whose Trading & Exchanges, served for so long as our touchstone for lucidly teaching about market structure, to the Fellows of the Columbia Program in the Law and Economics of Capital Markets, and to our colleagues at Columbia University and the University of Michigan. Most of the chapters in this book reflect work previously published in article form, although all have been extensively revised and much has not been published before. Thanks to the editors of those articles and to those cited in their acknowledgments.