THE UNIVERSE HAS A DESIGN, and so does a book. But unlike the universe, a book does not appear spontaneously from nothing. A book requires a creator, and that role does not fall solely on the shoulders of its authors. So first and foremost we’d like to acknowledge and thank our editors, Beth Rashbaum and Ann Harris, for their near-infinite patience. They were our students when we required students, our teachers when we required teachers, and our prodders when we required prodding. They stuck with the manuscript, and did it in good cheer, whether the discussion centered around the placement of a comma or the impossibility of embedding a negative curvature surface axisymmetrically in flat space. We’d also like to thank Mark Hillery, who kindly read much of the manuscript and provided valuable input; Carole Lowenstein, who did so much to help with the interior design; David Stevenson, who guided the cover to completion; and Loren Noveck, whose attention to detail has saved us from some typos we would not like to have seen committed to print. To Peter Bollinger: much gratitude for bringing art to science in your illustrations, and for your diligence in ensuring the accuracy of every detail. And to Sidney Harris: Thank you for your wonderful cartoons, and your great sensitivity to the issues facing scientists. In another universe, you could have been a physicist. We are also grateful to our agents, Al Zuckerman and Susan Ginsburg, for their support and encouragement. If there are two messages they consistently provided, they were “It’s time to finish the book already,” and “Don’t worry about when you’ll finish, you’ll get there eventually.” They were wise enough to know when to say which. And finally, our thanks to Stephen’s personal assistant, Judith Croasdell; his computer aide, Sam Blackburn; and Joan Godwin. They provided not just moral support, but practical and technical support without which we could not have written this book. Moreover, they always knew where to find the best pubs.