Publisher Summary This chapter discusses the chain of events that occurs during protein synthesis. The general reaction scheme is presented: the smaller subunits of ribosomes (30 S or 40 S subunits) attach to the initiation codon together with initiator tRNA (formyl methionyl tRNA for bacterial systems and methionyl tRNA for higher organisms). To this complex the larger subunits (50 S or 60 S subunit) bind to form the initiation complex of 70 S (or 80 S) ribosomes, initiation codon, and initiator tRNA. In this initiation process at least three initiation factors and GTP are involved. The chain then elongates as a result of the concerted action of three soluble factors, ribosomal peptide synthetase, aminoacyl tRNA, and 2 GTP molecules. When ribosomes carrying peptidyl tRNA reach the termination codon in mRNA, the termination factor binds to the ribosome–codon complex with the help of another soluble factor. At this point the chain is released from tRNA and the complex of mRNA, ribosome, and tRNA remains behind. The chapter also discusses the formation and structure of ribosomes and the formation of aminoacyl tRNA.