Assembling a program in bioinorganic chemistry that is scientifi­ cally relevant, well defined, and self-consistent is not an easy task. In this attempt we decided to consider zinc enzymes, copper oxidases, cytochromes and cytochrome oxidase. The choice is in part due to the great attention that the current specialized literature devotes to these topics, which are now debated among chemists, biochemists, biophysicists, etc .. We believe that hydration reactions, hydrolytic and oxidative processes have much in common from the point of view of the reaction mechanisms, the comprehension of which represents a frontier of science. For these reasons these topics have been the subject of the NATO-ASI held at San Miniato, Pisa, Italy, from May 28 to June 8, 1982. We hope we can transfer here the main conclusions of what (we believe) was a very stimulating scientific meeting. We would like to thank the local saving bank, Cassa di Risparmio di San Miniato, for helping in many ways. The financial contribution from the European Research Office of the US Army, and from the Bruker Spectrospin s.r.l., Italy, is also acknowledged. The National Science Foundation of the United States has provided a travel grant to one of the participants from the U.S.A. We are grateful to the NATO Scientific Affairs Division which provided a grant to finance this Institute.