The authors are grateful to the many pathologists who over the years have submitted interesting cases for consultation, providing the authors with a broad experience in the subject matter of this Fascicle. The reviewers of the initial manuscript offered many helpful suggestions, which have enabled us to improve the clarity of the text. We owe special thanks to Dr. Debra A. Bell and Dr. Judith A. Ferry of the Massachusetts General Hospital and Dr. Arthur L. Herbst of the Chicago Lying-In Hospital for reviewing specific sections of the text. Mrs. Marlene Fairbanks typed the manuscript and Mr. Stephen Conley and Ms. Michelle Forrestall provided photographic assistance. Finally, we wish to thank the editorial staff of UAREP for their support and patience. Robert E. Scully, M.D. Robert H. Young, M.D., FRCPath Philip B. Clement, M.D.