In the past twenty years, the X-ray crystallography of organic molecules has expanded rapidly in two opposite directions. One is towards larger and larger biological macromolecules and the other is towards the fine details of the electronic structure of small molecules. Both advances required the development of more sophisticated methodologies. Both were made possible by the rapid development of computer technology. X-ray diffraction equipment has responded to these demands, in the one case by the ability to measure quickly many thousands of diffraction spectra, in the other by providing...