This book is based on an advanced course of lectures on ribosome structure and protein biosynthesis that I offer at the Moscow State University. These lectures have been part of a general course on molecular biology for almost three decades, and they have undergone considerable evolution as knowledge has been pro gressing in this field. The progress continues, and readers should be prepared that some facts, statements, and ideas included in the book may be incomplete or out of-date. In any case, this is primarily a textbook, but not a comprehensive review. It provides a background of knowledge and current ideas in the field and gives ex amples of observations and their interpretations. I understand that some interpre tations and generalizations may be tentative or disputable, but I hope that this will stimulate thinking and discussing better than if I left white spots. The book has a prototype: it is my monograph "Ribosome Structure and Pro tein Biosynthesis" published by the Benjamin/Cummings Publishing Company, Menlo Park, California, in 1986. Here I have basically kept the former order of pre sentation ofthe topics and the subdivision into chapters. The contents ofthe chap ters, however, have been significantly revised and supplemented. The newly writ ten chapters on translational control in prokaryotes (Chapter 16) and eukaryotes (Chapter 17) are added.