This book began life as a review article. That article spawned a symposium which was, in turn, greatly expanded to form the present volume. As the project moved through these developmental stages (hopefully, towards attainment of its full maturity), a number of people have provided invaluable assistance to us, and we would like to take this opportunity to thank them. Gordon Orians must certainly take a high place in that list. He has been both a friend and mentor to W.E.K., and many of the topics explored in this book have emerged from the resultant dialogue. His thought processes, ideas and...