This book summarizes the most recent aspects of polycrystalline semiconductors as presented at the conference Polycrystalline Semiconductors - Grain Boundaries and Interfaces. It contains 12 review articles on selected topics written by experts in their fields and 41 complementary contributed papers. The structure, chemistry and physics of grain boundaries and other interfaces are experimentally and theoretically studied. Aspects of the technologically important polycrystalline silicon are discussed in detail. Also covered are other polycrystalline semiconductors, germanium and compound semiconductors, that are currently of interest in fundamental research and in the technology of solar cells and thin film devices. Anyone interested in polycrystalline semiconductors will be able to use this comprehensive collection to advantage. It also suggests directions for new research and development.