This chapter provides an introduction of IV-VI semiconductors. In addition to binary and ternary lead and tin chalcogenides, a number of mixed crystals with admixtures like the rare earth Eu or the alkali earth Sr make up the IV-VI material family. This group of compounds forms narrow gap multi-valley semiconductors. IV-VI crystals present one of the rare naturally occurring semiconductors, being used in early technical devices like electronic rectifiers and lead salt infrared detectors. Their main commercial uses are as detector elements and mid infrared lead salt laser diodes. The name lead salts for the IV-VI semiconductors are in common use in infrared optronics.