Knowledge of the structures of macromolecules is of major importance both to basic science and to new, burgeoning industries. The determination of these structures is improving our understanding of fundamental biological processes, and so it sets the stage for the broad explanation of diseases on the molecular level and for the rational design of drugs. It promises to give insight into such topics as the mechanisms of enzyme action, the implications of protein structure for evolutionary development, the relation of amino acid sequences to three‐dimensional structure and the relation between structure and function in complicated systems such as viruses, muscle, ribosomes and chromatin.