This book, which results from the dramatic increase in interest in the control mechanism employed in gene expression and the importance of the regulated proteins, presents new information not covered in Translational Regulation of Gene Expression, which was published in 1987. It is not a revision of the earlier book but, rather, an extension of that volume witl, special emphasis on mecha nIsm. As the reader will discover, there is enormous diversity in the systems employing genes for translational regulation in order to regulate the appearance of the final product-the protein. Thus, we find that important proteins such as protooncogenes, growth factors, stress proteins, cytokines, lymphokines, iron storage and iron-uptake proteins, and a panorama of prokaryotic proteins, as well as eukaryotic viral proteins, are translationally regulated. Since for some gene products the degree of control is greater by a few orders of magnitude than their transcription, we can state that for these genes, at least, the expression is translationall y controlled. Translational regulation of gene expression in eukaryotes has emerged in the last few years as a major research field. The present book describes mechanisms of translational regulation in bacteria, yeast, and eukaryotic viruses, as well as in eukaryotic genes. In this book we try to provide in-depth coverage by including important examples from each group rather than systematically including all additional systems not described in the previous volume.