The winter school on Localization and Confinement of Electrons in Semicon ductors was the sixth of a series dealing with new developments in solid~state physics organized by the Austrian Physical Society. The school, which was held in the castle of Mautemdorf, in the federal province of Salzburg, Austria, February 19-23, 1990, was attended by about 200 participants. This is the fourth such winter school to have the proceedings published in the Springer Series in Solid-State Sciences, the earlier ones appearing as Vols. 53, 67 and 83. The contributions of the invited speakers are arranged in seven parts according to topic: quantum boxes and quantum wires; localization and the metal-insulator transition; the integer and fractional quantum Hall effects and electron-electron interactions; tunneling and localization in low-dimensional structures and superlattices; optical properties of confined systems; impurities in quantum well structures; and optical and magnetic properties of dilute mag netic semiconductor quantum well. structures. A particular intention of this book is to present relevant introductory articles alongside the most recent research reports, all written by experts in the fields of localization and condensation of electrons in semiconductors, the quantum Hall effect, lateral superlattices, ballistic transport, etc. The fascinating subject of quantum boxes (dots) and quantum wires is treated in considerable detail. Experimental techniques for producing later ally structured two-dimensional electron gas systems are described together with methods for studying their electrical and optical properties.