I prepared this preface to the fourth edition of Viral Infections of Humans alone and with mixed emotions. It was immensely gratifying when Al Evans invited me to join him in producing the new edition. After following at a distance his exemplary career as a scholar and gentleman in every sense of those words, I was filled with anticipation at the privilege of observing close at hand the thoughtful dedication he had previously brought to editorial process. However, work together soon the our was overshadowed by the condition that would slowly take him from our task and our midst. As we both increasingly realized that his declining health might prevent him from seeing this final product, the initial gratification that I had felt gave way to a sense of awesome responsibility for perpetuating his masterful blend of science and literacy. From the earliest days in the planning of this revision, Al and I recognized the profound changes taking place both in the knowledge of viral infections and in the way that knowledge was being gathered. With all of biomedical science moving in the rush of revolution, every discipline generating information relevant to this text-from virology, immunology, and pharmacology to epidemiology and neuropsychology-has been swept along in the torrent, propelled principally by two synergizing technologic forces: molecular biology and cybernetics.