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 perhaps even some of his turns of phrase emerge throughout much ofthe book. Gordon also played a pivotal role in inviting in motion, and so he has served as a catalyst the article that set this project to the book as well as one of its reagents. While he has not served as an editor of this book, he is one of its authors in more than just the literal sense.