It has been 10 years since the Plenum Publishing Corporation printed a series of review articles on bacteriophages in Comprehensive Virology. Articles in that series contained physical-genetic maps but very little DNA sequence information. Now the complete DNA sequence is known for some phages, and 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 M13 for cloning and DNA sequencing by the dideoxy termination method. Also during this period the use of alter­ native sigma factors by RNA polymerase has become established for and T4. This seems to be a widely used mechanism in bacteria, SPO 1 since it has been implicated in sporulation, heat shock response, and regulation of nitrogen 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 chapters 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 pro­ vide comprehensive pictures of individual phage families and should pro­ vide valuable information for use in planning experiments.