This book stems from an Advanced Study Institute on Chromo somal Proteins and Gene Expression that was held in Sitges, Spain, on September 17-26, 1984. It would be misleading to call this volume a conference proceedings, however. The ASI was not a conference, but a course with diverse activities, only one of which was a set of major presentations by the lecturers. Indeed, the concept of lecturer was intentionally obscured as we all learned from each other through shorter presentations by other participants and through seminars, poster sessions, and small group discussions. Furthermore, many participants found that exchanging ideas outside organized sessions was among the most rewarding aspects of the course. Some even claimed to have profitably probed the intricacies of nucleosome structure and transcriptional regulation while basking in the sun on the beachl Obviously, it is difficult to catch the flavor of such varied proceedings in a book. (I cannot confirm the incident on the beach, never having found time to set foot there. Such is the fate of the director of a meeting. ) The ASI was judged a success -- and enthusiastically so - by most participants. Not only did we deepen our understanding of our scientific field, we made new friends and learned about scientific and nonscientific aspects of life in other countries and about issues that transcend international boundaries in our complex world. We hope that this volume will be as successful as the course was."