Science is a wonderfully resilient venture. There are new and interesting developments to report in each revision of this book, and this revision includes much updated mate-rial to account for new findings in molecular research. The general organization of material in this edition has been revised along the same lines as Essential Genes, making it easier to use the two books in conjunction. With increas-ing size becoming a problem, the content has been more sharply focused on genes and their expression by eliminat-ing the chapters dealing with the consequences of gene ex-pression for cell biology. Striking changes occur in the first part of the book, dealing with genomes, resulting from the success of many genome sequencing projects. The impor-tance of RNA as a regulator has become increasingly evi-dent and now can be seen to extend across all levels of gene expression in both prokaryotes and eukaryotes. Somewhat of a "missing link," it casts further light on how the current apparatus for gene expression must have evolved from the early RNA world.