Professor McMaster is a Biological Inorganic Chemist with interests in the roles of d-transition metals in biology. The progress in protein X-ray crystallography and spectroscopy has lead to detailed static pictures for the structures of the active sites of numerous metalloproteins. As a result, a major challenge for the bioinorganic chemist is to understand the properties and functions of metalloenzymes within this well-defined structural framework. Ultimately, insight into the properties of biological metal centres derives from a description of the electronic structure of the active site and how other enzyme motifs perturb it. Parallel with the advances in physical methods has been the constant discovery of new biological systems containing metal ions in environments that have no precedent in coordination chemistry. Consequently, not only is the field becoming more detailed but its breadth is also increasing, providing new challenges for the synthetic inorganic chemist.