The International School on Crystallographic Computing was held at the Bischenberg Congress Center, close to Strasbourg, in 1990. This was the twelfth such school organized since 1960 under the auspices of the IUCR Commission of crystallographic computing. The school was a satellite meeting to the XVth Congress of the International Union of Crystallography in Bordeaux, at which lecturers and tutors gave conferences and demonstrated their programs. In selecting the contents of the school, the program committee took into account the increasing emphasis on the study of macromolecules of biological interests, a natural progression of the clear success of crystallographic methodology in small molecule crystallography. Themes covered include synchrotron data collection, the potentiality of imaging plate technology coupled with efficient software, maximum entropy phasing methods, refinement using molecular dynamics, and map interpretation using structural databases. This is the latest volume in a series of highly regarded volumes based on lectures given at the International School of Computational Crystallography. Here, international contributors have collaborated to provide a unique record of the state-of-the-art in this important area of crystallography.