The role of hydrothermal fluids during the crystallization of layered intrusions and the ore deposits they contain has long been debated. This book summarizes the evidence for fluid-crystal-liquid (hydromagmatic) interactions and their importance for the understanding of the formation of platinum-group deposits in layered intrusions. It discusses the composition of igneous fluids in mafic magmatic systems, the generation and movement of these fluids in layered intrusions, their impact in altering the mineralogy and composition of the originally precipitated assemblages, and their role in the transport of the platinum-group elements (PGE). Using examples from the Bushveld complex of South Africa and other intrusions, this book provides a comprehensive overview of the hydromagmatic model for the origin of various features of layered intrusions. It is a useful reference for academic researchers and professional geologists working on economic mineral exploration, layered igneous intrusions, and hydrothermal metallogenesis.