The last decade has seen a remarkable flourishing of the biological structure field. This blossoming has brought an explosion of stereochemical information, and has been made possible by the combined improvement in techniques of X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, and the bulk preparation of biological materials. Most crucial, however, has been the desire of the experimental biologists to follow research problems to the level of stereochemistry, which is the ultimate reductionist limit of molecular biology. This aim has been driven by the anticipation that such knowledge may permit better understanding and even engineering of biological function.