The scope of detector materials for semiconductors and scintillators includes a wide variety of molecular compounds such as cadmium zinc telluride (CZT), lanthanum halides, and others. An additional class of scintillators is based on organic compounds and glasses. Ideally, attributes of materials used for radiation detection include appropriate-range bandgaps, high atomic numbers of the central element, high densities, performance at room temperature, strong mechanical properties, and low production cost. Unfortunately, there are significant gaps in the knowledge required to produce radiation detection materials of higher quality - in terms of reproducible purity, homogeneity and mechanical integrity. This book explores results in radiation detection materials from both experimental and theoretical standpoints, as both are needed to grow and characterize materials that will produce better detectors in the future.