This monograph is neither a historical outline of the development of the concepts of protein biosynthesis and the structure and functions of the ribosomes, nor an exhaustive survey of the literature on these questions. The monograph is based upon an analysis of the modern trends in this field. The purpose of the monograph was to formulate more or less generalized representations of the structure and" function of the ribosome, as we envision it at the present day. It may be that this attempt is premature for a number of reasons, and the concepts outlined here will very soon be revised....