ng the insights of the economics of product differentiation and congestion. Acknowledgments Daniel F. Spulber gratefully acknowledges the support of a research grant from the Searle Foundation that made his contribution to this book possible. Spulber also thanks Dean Dipak Jain and Dean Kathleen Hagerty for their support of his research work, and he thanks the Kellogg School of Management for providing a stimulating research environment. Christopher S. Yoo gratefully acknowledges a grant from the Milton and Miriam Handler Foundation, which helped support his contribution to this book. He also thanks Deans Kent Syverud and Edward Rubin of the Vanderbilt Law School, Dean Michael Fitts of the University of Pennsylvania Law School, and his colleagues at both institutions for their support and encouragement. In addition to acknowledg- ment of his wife in the dedication, he also would like to express his appreciation to his children, Marshall and Brendan, who fill his life with such joy every day. Both would like to thank Johannes Bauer, Mark Brandon, Jon Bruce, David Callies, K.C. Chiu, Andrew Daughety, Paul Edelman, James Ely, Joseph Farrell, Gerald Faulhaber, Rob Frieden, Brett Frischmann, Luke Froeb, Chris Guthrie, Todd Henderson, Jack Hirshleifer, Herbert Hovenkamp, Charles Jackson, Louis Kaplow, Vik Khanna, Jeff MacKie-Mason, Elliot Maxwell, Richard Nagareda, Randy Picker, Richard Pierce, Robert Rasmussen, Jennifer Reinganum, Jim Rossi, Greg Sidak, Robert Thompson, Michael Vandenbergh, Philip Weiser, Sang-Seung Yi, Kiho Yoon, and participants in workshops conducted at the American Law and Economics Association, Seoul National University, the Telecommunications Policy Research Conference, UCLA Law School, the University of Michigan, the University of Pennsylvania, Vanderbilt University, the Wharton School, and Northwestern University for their comments on earlier versions of this work. Elizabeth Mc- Intyre, David Nijhawan, Robert Schmoll, and Constantin Severe provided excellent research assistance. The book was p