Transition metal ions in biological systems are of interest in biology, biochemistry, chemistry, medicine, and physics. Scien tists with rather different viewpoints, employing many methods, have contributed to this area. A concise review of the current state of the field will, to some extent, reflect the special knowledge of the person writing it - in this case application of physical methods to the investigation of metal coordination. x ray diffraction is one of the most important of these methods, but a useful treatment of X-ray structure analysis would be com parable in size with and...