In 1963, the first edition of Chemistry of Viruses was published as a contribution to the series on viruses sponsored by Protoplasmatologia. An aim of the first edition was to review some major principles and techniques of chemical virology in a concise manner and to accompany this review with a compilation of pertinent references. It was anticipated that this exercise would be helpful to the author in his teaching and research and, hopefully, would be useful to readers as well. The literature of virology has grown enormously since then, and it is even more urgent to have a succinct survey. In addition, few authors have attempted to integrate the findings pertaining to the various major classes of viruses (that is, animal, bacterial, and plant viruses) but, rather, have chosen to assemble large monographs dealing in depth with facts and fancies pertaining to specific groups of viruses. Such works are valuable for pursuit of particular topics but fail to yield a brief, integrated view of virology. The present edition of Chemistry of Viruses aspires to such a review. A serious attempt was made to deal concisely with every major topic of chemical virology and to present examples from different classes of viruses. Numerous references are given to original articles and review papers as well as to selected books.