Michael Robb is well known for applying quantum mechanics to chemistry. He has contributed methodological developments as well as applications to the chemical reactivity of organic molecules. Michael and his co-workers were the first to apply multiconfigurational methods to elucidate the mechanisms of organic multibond reactions. His recent work on photochemical problems is particularly distinguished; he has established a new theoretical foundation for this subject by demonstrating that real surface crossings are the central feature of most photochemical processes, in contrast to the previously held view that such processes are rare.