Originally, it was our intention to produce a single-volume book covering all aspects and approaches to the problem of specific inhibitors of respiratory viruses. However, as the work progressed it became obvious that certain chapters, because of the research interests of the authors, concentrated particularly on influenza viruses. It seemed logical therefore, to divide the book into two volumes, the first emphasizing influenza and the second concentrating on other viruses as well as discussing important general aspects of drug screening and clinical testing, although the second volume does have some chapters which deal mainly with influenza.