This book is directed primarily to advanced graduate and medical students, postdoctoral trainees, and established investigators having basic research interests in neoplasia. Its content is based in part on the lecture outlines and selected histopathology laboratory components of an advanced course entitled The Pathobiology of Experimental Animal and Human Neoplasia, developed by me for the Experimental Pathology Curriculum of the Department of Pathology at the Medical College of Virginia. In this regard, an effort has been made to integrate pathology with carcinogenesis, genetics, biochemistry, and cellular and molecular biology in order to present a comprehensive and current view of the neoplastic process. For focus, emphasis is mainly being placed on the neoplastic cells themselves, and not on associated host-mediated responses. It ishoped that this book will accomplish its purpose of providing students and researchers who already possess strong but diverse basic science backgrounds with unifying concepts in tumor pathobiology, so as to stimulate new research aimed at furthering our understanding of neoplastic disease. I wish to express my appreciation and heartfelt thanks to the authors, whose individual ranges of expertise and research experience clearly bring to their respective chapters unique perspectives that easily transcend any redundancy that may be present. In addition, I am grateful to Drs. George Vennart, Saul Kay, and Fred Meier, and to Ms. Connie Wilkerson of the Department of Pathology at MCV, for their helpful comments and their review of some of the material.