The oncogenic virus can only be studied as a carcinogen when its relation to the host cell in which it resides is understood. The interaction between tumor virus and host cell was the subject of a recent North Atlantic Treaty Organization Advanced Study I~stitute. This volume is the edited proceedings of this study institute. One problem of fundamental importance in understanding malignant transformation is the mechanism by which the oncogenic vector promotes the aberrations in the host cell regulatory appara­ tus resulting in a cancerous cell. It is partly the purpose of this volume to help clarify this problem, and to stimulate the interest of others to continue the research necessary to this end. The meeting from which this volume is compiled took place in the Principality of Monaco with the patronage of Her Serene High­ ness, Princess Grace and was supported principally by a grant from the North Atlantic Treaty Organization. The editor wishes to thank the North Atlantic Treaty Organization, Princess Grace of Monaco, and the Bureau de Tourism Monaco for their generous support. Addi­ tional financial assistance was provided by the Deutsches Studium Gesellschaft and I would like to thank Prof. Klaus Munk, Deutsches Krebsforschungszentrum, for his help in obtaining this aid. I would also like to thank the Verwaltung of the Deutsches Krebsfor­ schungszentrum for their administrative help.