Threonine, one of proteinogenic as well as essential amino acids, is classified as polar and uncharged residue, which may play an important role in intermolecular interactions between protein molecules and small ligand molecules. This book includes chapters on the lysozyme of egg white, which contains seven threonine residues in the primary structure; the requirements of threonine for laying hens fed diets with increasing levels of threonine at variable and constant ratios; the role threonine may potentially play in intermolecular interactions towards ligands of small molecules and the highly mutated threonine-producer strains, and ways of optimization and intensification of its biosynthesis.