Significant advances have occurred in the theory of non-stoichiometry problems and fundamentally new and wide-ranging applications have been developed, helping to better identify relevant issues. The contributions in this volume bring together the experience of specialists from different disciplines (materials scientists, physicists, chemists and device people) confronted with non-stoichiometry problems. The 40 papers, including 9 invited papers, give an advanced scenario of this wide interdisciplinary area, which is highly important in its diverse aspects of theory, implementation and applications. This work will be of interest not only to universities and laboratories engaged in studies and research in this field, but also to organizations and industrial centres concerned with implementations and applications. The diversity of the topics, as well as the extraordinary tempo in which Non-stoichiometry in Semiconductors has progressed in recent years attest to the permanent vitality of this field of research and development.