This is the latest massive tome of the new Bergey, and deals exclusively with the Phylum Firmicutes, the low G+C Gram-positive bacteria, and excludes the Mollicutes and Actinobacteria. It is a monumental achievement: the dedication, patience and fortitude of the editors and contributors cannot be understated, in that they have achieved a definitive benchmark for the understanding of the biodiversity of the phylum, and provided the most authoritative single source of systematic information about these organisms. As it went to press in late 2007, it is inevitably 'out-of-date' with respect to genera and species described since, but this in no way detracts from its value as a reference source. In this regard, a bonus is its 104-page appendix (by Jean Euzéby), listing all the organisms described in International Journal of Systematic and Evolutionary Microbiology since volume 2 was published. The information explosion in microbial taxonomy and systematics in recent decades means that the older single volumes of Bergey which sat easily on the laboratory shelf are no more, both because of bulk and cost, but this volume is an essential purchase for University and Technical libraries and larger institutional departments. It is not a book to sit and read, but it is fascinating to dip into just to see the sweep of advance of the systematics of this group. Its readership has to be all microbiologists, molecular biologists and medical and environmental researchers, as a first call on all questions relating to Firmicutes. It is conceivable that this may be the last time such on-paper publication of Bergey's Manual will be possible, as the seemingly exponential rate of increase in the size of the Manual may dictate that electronic publication (with the benefits of instant update and availability) may become the norm for future editions. It will, however, be a sad day when volumes for browsing like this one disappear from the shelves.