The genus Bacillw; has a long history of importance, both from an economic point of view and as a source of experimental microorganisms. This volume critically reviews aspects of identification, molecular biology, and growth that are of impor tance for the current and anticipated future exploitation of members of this group. In addition, the volume includes a chapter on taxonomy, as the importance of good taxonomy is often not fully appreciated; on sporulation, since so many important products are produced concomitantly with this process and we are beginning to understand the mechanisms by which the process is controlled; and, finally, on the cell envelope, as we are only just beginning to appreciate the significance of dif ferences between the cell walls of gram-positive and gram-negative bacteria for productivity and processing. The commercial importance of Bacillus lies mainly in the area of enzyme pro duction for the food, drink, and detergent markets. Increasingly, however, the ability of Bacillus to secrete proteins, coupled with its regulatory acceptability, has resulted in strenuous efforts to develop species of Bacillus as hosts for the produc tion of value-added heterologous proteins. Difficulties have often been encoun tered, indicating a need to divert more resources to improving our understanding of the molecular biology of members of this grou p. Experience with Escherichia coli, a far from ideal organism from a commercial point of view, suggests that an in creased investment in Bacillus is likely ultimately to be productive.