The study of tumor markers is not only one of the most important but also one that offers one of the richest perspectives in biology and clinical oncology. The aim of scientists in this field is to adduce evidence of a property that is typical of and exclusive to tumor cells, and which is easy to determine, in order to immediately recognize, or even better, to foresee, neoplastic transformations. Unfortunately, despite the large number of scientists and laboratories engaged in this work, the ideal tumor marker has not yet been identified. However, it is worth noting that new trends in molecular biology and immunovirology have recently opened up new avenues that may lead to the eventual resolution of this problem. In this book, different approaches to the identification of tumor markers, from the points of view of biochemistry, immunology, and molecular biology, are compared in order to explore possible interrelationships and to stimulate scientific collaboration among scientists active in these fields, both in basic research and in clinical applications. We wish to thank all the contributors and also the publisher, especially Dr. Robert Andrews, for making the publication of this book possible.