During the last twenty years condensed matter physics has been revolutionized by a number of developments. The advent of the renormalization group approach to phase transitions has provided a framework for the discussion of systems in which many length scales play an important role. The development of large scale computers has allowed theorists to carry out significant simulations of realistic models of materials. The continuing discovery and design of new materials such as high temperature superconductors and semiconductor heterostructures and nanostructures has provided a vast range of new phenomena (Quantum Hall effect, mesoscopic devices, high Tc materials) which have fueled theoretical activity.