AbstractProteins are the most versatile of the bipolymers with respect to structure, properties and function. This versatility is a consequence of the chemical diversity of their amino acid monomers and of the infinite number of ways in which the amino acid composition, linear sequence and three‐dimensional folding may be varied. The constituent amino acids include hydrophobic and hydrophilic, reactive and inert forms. Thetrans, planar nature of the amido (peptide) linkage between amino acids limits the conformational freedom of the resulting polypeptide chain. Portions of the chain usually occur as one of several regular forms such as helixes, stabilized by hydrogen bonds. Overall conformation of the molecule is maintained largely by noncovalent forces such as hydrogen bonds and hydrophobic interactions. Conformation of the protein is determined by the linear sequence of amino acids in the chain, but is readily interrupted by a variety of nonphysiological agents, with concurrent loss of biological function. This rearrangement of the polypeptide chains, denaturation, usually results in an alteration of the characteristic chemical and physical properties of the molecule. The observation that denaturation can sometimes be reversed leads to new concepts of protein structure and properties.