Volume 62 of Reviews in Mineralogy and Geochemistry reviews the recent research in the geochemistry and mineral physics of hydrogen in the principal mineral phases of the Earth's crust and mantle. Contents: Analytical Methods for Measuring Water in Nominally Anhydrous MineralsThe Structure of Hydrous Species in Nominally Anhydrous Minerals: Information from Polarized IR SpectroscopyStructural Studies of OH in Nominally Anhydrous Minerals Using NMRAtomistic Models of OH Defects in Nominally Anhydrous MineralsHydrogen in High Pressure Silicate and Oxide Mineral StructuresWater in Nominally Anhydrous Crustal Minerals: Speciation, Concentration, and Geologic SignificanceWater in Natural Mantle Minerals I: PyroxenesWater in Natural Mantle Minerals II: Olivine, Garnet and Accessory MineralsThermodynamics of Water Solubility and PartitioningThe Partitioning of Water Between Nominally Anhydrous Minerals and Silicate MeltsThe Stability of Hydrous Mantle PhasesHydrous Phases and Water Transport in the Subducting SlabDiffusion of Hydrogen in MineralsEffect of Water on the Equation of State of Nominally Anhydrous MineralsRemote Sensing of Hydrogen in Earth's Mantl