IV–VI and IV–VI2 semiconductors have attracted considerable attention due to their applications in the fabrication of electronic and optoelectronic devices as light-emitting diodes and solar cells. The electrical properties of these semiconductors can also be tuned by adding impurity atoms. Because of their wide application in various devices, the search for new semiconductor materials and the improvement of existing materials is an important field of study. Doping with impurities is a common method of modifying and diversifying the properties of physical and chemical semiconductors. This book covers all known information about phase relations in quaternary systems based on IV–VI and IV–VI2 semiconductors, providing the first systematic account of phase equilibria in quaternary systems based on IV–VI and IV–VI2 semiconductors and making research originally published in Ukrainian and Russian accessible to the wider scientific community. This book will be of interest to undergraduate and graduate students studying materials science, solid-state chemistry, and engineering. It will also be relevant for researchers at industrial and national laboratories, in addition to phase diagram researchers, inorganic chemists, and solid-state physicists.