This U.S.-Italy award will support an international school--a combined workshop and seminar meeting--covering recent advances in the understanding of static, kinematic and dynamic aspects of crystal and molecular structure, as studied by crystal diffraction, spectroscopic and theoretical methods. The school is being held at the Ettore Majorana Centre for Scientific Culture in Erice, Sicily, from May 30 to June 9, 1991 and is being organized by Professor Kenneth Trueblood of UCLA for the U.S. side and Professor Lodovico Riva di Sanseverino of the University of Bologna for Italy. About 120 participants from a dozen or more countries are expected, the great majority of whom will be young faculty members or others who have recently received advanced degrees. There will be about 20 lectures and 10 tutors to help in workshops and microsymposia. During the last two decades, the amount of precise and accurate information about molecular structure has increased enormously. Much of this is the result of increased automation and precision of data collection and analysis in crystal diffraction, but there have also been important advances in other experimental techniques for studying structure. In addition, theory has progressed to a stage where some of the details of molecular structure can be predicted at a level comparable with that attained by experiment. There have also been advances in the analysis of the kinematics and dynamics of molecules in crystals, as well as in their correlation with phase transforma- tions and solid state reactions. The present school intends to review past achievements, present projects, and future goals in the realm of crystal and molecular structure studies by diffraction and spectroscopic methods. Particular emphasis will be placed on the description and understanding of atomic motion in molecules and in crystals, with relevance to physical properties, chemical reactivity, and phase transformations, including such topics as structure-correlation (using statistical methods with the Cambridge Structural Database), polymorphism, and solid-state reactions.