This volume comprises the compounds of thorium with silicon, phosphorus, arsenic, antimony, bismuth, and germanium. Many of the compounds treated in this volume are of specific technological interest, mainly in the nuclear field. Refractory compounds like ThSi or ThP have potential interest as nuclear fuel for special reactors due to their physical properties like good heat conductivity and their chemical stability, e.g., against the corrosion of cladding alloys for nuclear fuel elements. For most of the binary and ternary phases in these systems, we presently have good knowledge about the preparation of the compounds and their physical and chemical properties. But nevertheless, there are still a lot of open questions concerning phase equilibria, solid solutions, and homogeneity of some the phases. Thorium phosphates and compounds with acidic organic phosphates and phosphonates are quite well investigated because some of them are formed in the THOREX process for reprocessing fuels of the thorium fuel cycle as a result of radiolysis and hydrolysis of the extractant tri-n-butylphosphate. The difficulties of investigation come from the fact that most of these compounds are difficult to get in crystalline form with well characterized properties. Some phosphates and hydrophosphates, e.g., are also often used in analytical chemistry to separate trace elements, like Pa specifically, from other radioactive elements.