difficult to find authors who are willing to write about areas outside those pursued in their own laborato­ ries. Anyone who takes on the task of reviewing a broad area of interest must weave together its various parts by picking up the threads from many different laboratories, and attempt to produce a fabric with a meaningful design. Finding persons who are likely to succeed in such tasks was the most difficult part of our job. In the first volume of this treatise, most of the chapters dealt with the mechanisms of regulation of gene expression in microorganisms. This second volume involves a somewhat broader area, spanning the prokaryotic-eukaryotic border.