This volume collects the contributions to the NATO Advanced Study Institute (ASI) held in Aussois (France) by March 25 - April 5, 1991. This NATO ASI was intended to present and illustrate recent advances in computer simulation techniques applied to the study of materials science problems. Introductory lectures have been devoted to classical simulations with special reference to recent technical improvements, in view of their application to complex systems (glasses, molecular systems . . . ). Several other lectures and seminars focused on the methods of elaboration of interatomic potentials...