This book provides a detailed study of the Atomic Layer Epitaxy technique (ALE), its development, current and potential applications. The rapid development of coating technologies over the last 25 years has been instrumental in generating interest and expertise in thin films of materials, and indeed the market for thin film coatings is currently £3 billion with projected annual growth of 20 to 30% [1]. ALE is typical of thin-film processes in that problems in the processing or preparation of good quality epitaxial films have been overcome, resulting in better performance, novel applications of previously unsuitable materials, and the development of new devices. Many materials exhibit interesting and novel properties when prepared as thin films and doped. Vapour-deposited coatings and films are used extensively in the semiconductor and related industries for making single devices, integrated circuits, microwave hybrid integrated circuits, compact discs, solar reflective glazing, fibre optics, photo voltaic cells, sensors, displays, and many other products in general, everyday use. The ALE technique was developed by a research team led by Tuomo Suntola, working for Instrumentarium Oy in Finland. The key members of this team were lorma Antson, Arto Pakkala and Sven Lindfors. In 1977, the research team moved from Instrumentarium to Lohja Corporation, where they continued the development of ALE and were granted a patent in the same year. By 1980, the technique was sufficiently advanced that they were producing flat-screen electroluminescent displays based on a manganese-doped zinc sulphide layer.