The third edition of this book has been completely revised and updated, and new chapters have been added on Hantanvirus by Karl Johnson, on retroviruses by William Blattner, and on hepatocellular carcinoma by Joseph Melnick. New authors have replaced previous authors for several chapters. These include Karl Johnson on arenaviruses, Stephen Hadler and Harold Margolin on viral hepatitis, Paul Glezen and Robert Couch on influenza, Alfred S. Evans and Guy de-The on Burkitt lymphoma, and Joseph Melnick, William Rawls, and Ervin Adam on cervical cancer. A summary of the major advances since the last edition in 1982 has been provided by each contributor as given below. Overall, it is clear that the rapid advances in molecular virology, monoclonal antibody, and rapid diagnostic techniques dominate the progress since the last edition and provide a better understanding of pathogenesis, newer tools for epidemiologic investigation, and new methods for vac cine production. Although there is repetition in mention of these advances as written by each contributor, the editor has let these stand to let the reader know how each interprets the impact of these new developments. I. Introduction and Concepts Chapter 1. Epidemiologic Concepts and Methods: The sections on control of infectious diseases has been much expanded to cover progress and problems in both developed and developing countries, the concepts of eradication and elimination, and the means to assess the need and effectiveness of immuniza tion programs."