A retrospective and chronological review will be presented of the scientific and technological evolution of metal/insulator/semiconductor structures with emphasis on the interfaces between compound semiconductors, homomorphic, heteromorphic, and heterojunction quasi-insulators. The Conference on the Physics and Chemistry of Semiconductor Interfaces has provided for the past 20 years a forum for the synthesis of worldwide research on the nature of dielectric/semiconductor interfaces. The current status of such research and some of the many unresolved fundamental and applications-oriented issues that remain to be explored will be introduced, as well.