The NATO Advanced Study Institute on "Interfaces, Quantum Wells and Superlattices" was held from August 16th to 29th, 1987, in Banff, Alberta, Canada. This volume contains most of the lectures that were given at the Institute. A few of the lectures had already been presented at an earlier meeting and appear instead in the proceedings of the NATO Advanced Study Institute on "Physics and Applications of Quantum Wells and Super lattices" held in Erice from April 21st to May 1st earlier in the year and published by Plenum Press. The study of semiconductor interfaces, quantum wells and super­ lattices has come to represent a substantial proportion of all work in condensed matter physics. In a sense the growth of interest in this area, which began to accelerate about 10 years ago and seems to be continuing, has been driven by technological developments. While the older generation of semiconductor devices was based on adjacent semiconductors with different properties (e. g. different doping levels) separated by interfaces, modern semiconductor devices tend to be based more and more on properties of the interfaces themselves. This has led, as an example, to the field of band-structure engineering. Improved understanding of the fundamental physics of these systems has aided technological developments and, in turn, technological developments have made available systems which exhibit novel and fascinating phYSical properties, such as the integer and fractional quantum Hall effects.