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-Th~ 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 contributoras given below. Overall, it isclearthat the rapid advances in molecularvirology, monoclonal antibody, andrapiddiagnostictechniquesdominatetheprogress sincethe lastedition andprovideabetter understanding of pathogenesis, newer tools for epidemiologic investigation, and new methods for vac­ cine production. Although there is repetition in mentionofthese advances as written by eachcontributor, 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 I. EpidemiologicConcepts and Methods: Thesectionsoncontrolofinfectiousdiseases has been much expanded to cover progress and problems in both developed and developing countries, the conceptsoferadicationandelimination, and the means to assess theneedandeffectivenessofimmuniza­ tion programs.