Chalcopyrite is the most abundant copper sulfide, the most recalcitrant to hydrometallurgical processing, and a good semiconductor with a wide variation in resistivity. The reactivity of chalcopyrite from different sources has been a controversial issue since the seventies. It is known that synthetic chalcopyrite is more reactive than natural samples. This book discusses the chemical composition, uses and occurrence of the copper iron sulfide mineral, chalcopyrite.