The Copley Medal is awarded to Sir John Cornforth, F. R. S. Sir John’s early research, conducted in Australia, was principally on natural products from plants. Later he came to work with Sir Robert Robinson at the University of Oxford on the chemistry of penicillin and steroids. The latter research culminated, in 1951 and simultaneously with that of R. B. Woodward in the United States of America, in the first total synthesis of non-aromatic steroids. About the same time, Cornforth also described the use of hecogenin starting-material for cortisone synthesis, and a new stereoselective general synthesis of olefines. Subsequently, with G. Popják, he made major contributions to the determination of the stereochemistry of reactions controlled by nicotinamide coenzymes. They also devised labelling methods to elucidate the stereochemistry of steroid and polyterpenoid biosynthesis, resulting in the definition in every detail of the stereochemistry of squalene biosynthesis. To do so, asymmetrically labelled mevalonates and, subsequently, asymmetrically labelled methyl groups were synthesized; this provided a technique to study the fine details and elucidate the stereochemistry of many enzymic reactions. In the 1950s Sir John also synthesized the mucopolysaccharide component, acetylneuraminic acid, and in the 1960s the plant hormone abscisic acid. At present, he is attempting to synthesize organic molecules specifically designed as enzyme-like catalysts of olefine hydration.