This book was conceived many years ago as an abstract goal for a father-son team when the father was working in university administration and the son was just getting into the academic business. Eventually, the father returned to the laboratory, the son began to get his feet on the ground, and the goal became concrete. Now the work is finished, and our book enters the literature as, we hope, a valuable contribution to understanding the terribly complex and subtle problem of the neuro­ biology of motivated behaviors. We would also like the book to stand as a personal mark of a cooperative relationship between father and son. This special relationship between the authors gave us an extra dimension of pleasure in writing the book, and it would delight us if it gave anyone else an extra dimension of enjoyment from reading it. One thing we hope happens is that anyone or simply considering entering similar considering a similar partnership, of this book as encouragement. Such re­ fields, will take the existence lationships are highly satisfying if both parties take care to protect the partnership. When we actually sat down to write the book, we were humbled by the immense literature and the smallness of both our conceived space for putting it down and of our brains for processing all the information.