This volume contains the proceedings of the International Winter School on "Heterostructures and Two-Dimensional Electronic Systems in Semiconductors." The school took place in Mauterndorf, Austria, from February 26 - March 2, 1984, and was the third one in a series of winter schools on "New Develop ments in Solid-State Physics," organized by the Austrian Physical Society, Solid State Physics Division. The school was attended by about 150 scientists from 12 countries, including the United States of America, Japan and Poland. Most of the research groups of Western Europe working in this field participated and demonstrated the still increasing interest in the topics. These topics cover the wide area ranging from fundamental phenomena in solid-state physics, like the quantum Hall effect, to new semiconductor devices, all based on two-dimensional elec tronic systems. We hope that the spirit of this school, the combination of basic and applied physics (including skiing) will stimulate further progress in this field of research. This conference was sponsored by the Austrian Physical Society, Austrian Federal Ministry for Science and Research, European Research Office of the US Army, European Office of Aerospace Research and Development, Federal Province of Salzburg, and Osterreichische Forschungsgemeinschaft Further financial support came from the following companies: Balzers, IBM Austria, Messer-Griesheim, Oxford Instruments, Klaus Schafer & Co., Siemens Osterreich and Varian."