The time seems ripe for a critical compendium of that segment of the biological universe we call viruses. Virology, as a science, having passed only recently through its descriptive phase of naming and numbering, has probably reached that stage at which relatively few new-truly new-viruses will be discovered. Triggered by the intellectual probes and techniques of molecular biology, genetics, bio- chemical cytology, and high resolution microscopy and spectroscopy, the field has experienced a genuine information explosion. Few serious attempts have been made to chronicle these events. This...