It has been 10 years since Plenum included a series of reviews on bacte­ riophages, in Comprehensive Virology. Chapters in that series contained physical-genetic maps but very little DNA sequence information. Now the complete DNA sequence is known for some phages, and the se­ quences for others will soon follow. During the past 10 years two phages have come into common use as reagents: A phage for cloning single copies of genes, and Ml3 for cloning and DNA sequencing by the dideoxy termi­ nation method. Also during that period the use of alternative sigma fac­ tors by RNA polymerase has become established for SPOl and T4. This seems to be a widely used mechanism in bacteria, since it has been implicated in sporulation, heat shock response, and regulation of nitro­ gen metabolism. The control of transcription by the binding of A phage CII protein to the -35 region of the promoter is a recent finding, and it is not known how widespread this mechanism may be. This rapid progress made me eager to solicit a new series of reviews. These contributions are of two types. Each of the first type deals with an issue that is exemplified by many kinds of phages; chapters of this type should be useful in teaching advanced courses. Chapters of the second type provide comprehensive pictures of individual phage families and should provide valuable information for use in planning experiments.