This volume, the proceedings of the First International Workshop on Electron Correlations and Materials Properties, held in June 28-July 3, 1998, provides experimental evidence of the effects of correlation on the physical, chemical, and mechanical properties of materials, as well as the theoretical/computational methodology that has been developed for their study. The volume focuses in particular on understanding in detail the quantum nature of the electronic states in solids pertaining to correlation effects and their impact on observable behaviour as provided by both band-theoretical and many-body approaches.