In this book we present a largely biochemical look at the metals of life and their functions, which we hope will be of interest to chemists and biologists as well as biochemists. The field of 'inorganic bio chemistry' is one of rapid change. Recent developments in our know ledge of the activity of calcium, and of the iron-sulphur proteins, are two examples, and increasing attention is being paid to non-metals as well [3]. For reasons of space, we shall restrict ourselves to the normal biological activities of metals. We must ignore, on the one hand, the gross physiological effects of metal deficiency or toxicity, and on the other, the many model studies which have been stimulated by the unusual properties of metals in biological systems. Usually the synthesis of model metal compounds follows rather than anticipates the dis covery of novel biological configurations. However, such studies give us a firm basis for an understanding of the biological systems, and sometimes answer questions that cannot be tackled any other way (for instance, what is the net charge on an iron-sulphur cluster?). As a result, we can refer to new and interesting information on the metals oflife at a chemical level. We gratefully acknowledge the help of Professor P. Banks and Dr D. Fenton who have read and criticized the manuscript, though any errors or misconceptions remain our own responsibility. We thank Mr P. Elliot for preparing Fig. 5.2.