The publication of this volume of The Viruses entitled The Togaviridae and Flaviviridae comes at an appropriate time. The structure and rep lication strategies of these viruses are now known to be sufficiently di verse to warrant the removal of flaviviruses from the Togaviridae family and establish them as an independent family. Flaviviridae have a special place in the history of virology. The prototype virus-yellow fever virus was the first virus to be identified as the cause of a human disease. Some of the history of this discovery is described in Chapter 1 of this volume; in Chapter 10 the...