We have selectively reviewed various aspects of protein and amino acid metabolism and nutrition which we feel are relevant and important in any comprehensive consideration of proteins, peptides, and amino acids in enteral nutrition. These, together with various clinical aspects of the problem that we have not addressed, are covered in more specific detail elsewhere in this volume. Our hope is that by the time this workshop is at an end a reasonable picture of the state of the art will emerge in terms of an understanding of the physiology and biochemistry of protein, peptide, and amino acids in enteral nutrition. Simultaneously, we will need to know, through careful clinical investigation, how this knowledge can best be exploited for optimizing the design of the protein/peptide/amino acid component of enteral nutrition formulations. In doing so it should be possible to achieve a more effective enteral use of proteins, peptides, and amino acids in the comprehensive clinical management of individuals under various pathophysiological states.