This book addresses the origin of gold deposits to answer questions of science and curiosity. These answers contribute in turn to the improved exploration and mining of gold. Initially there is a summary of the methods used to address the genesis of gold deposits including some of the essential science and concepts. Five basic observations follow that apply to many gold deposits and need to be considered in any genetic ideas. Magmatic processes enriching gold are discussed followed by the role of aqueous fluids during gold deposit formation at elevated temperatures and pressures. Modifying effects after deposit formation include high-grade metamorphism, retrogression, weathering, and erosion. The main types of gold deposits are then explained within the spectrum of viable genetic ideas, with informal names for these examples that include gold-only, gold-plus, Carlin, slate-belt, epithermal, porphyry, iron oxide copper gold, and Archean greenstone. Case histories are included in which the role of gold geology contributed directly to discoveries—one example is at the province-scale and another at the goldfield-scale. Unlike other books on the subject, this one addresses virtually all gold deposit types rather than focusing on one type in isolation. The primary readership includes industry geologists, senior undergraduates, postgraduates, and those with some knowledge of science and an interest in the gold industry.