This book presents a summary of high-pressure phase transitions of minerals and related inorganic compounds. The first part reviews the methods to investigate phase transitions by direct high-pressure and high-temperature experiments together with thermodynamic approaches that consist of calorimetric measurements and thermodynamic calculation. In the second part, phase relations and thermodynamic properties of olivine, pyroxene, garnet, spinel, perovskite, rutile, and related inorganic compounds with A2BO4, ABO3, AB2O4, and AO2 stoichiometries are described. Particular emphasis is placed on spinel- and perovskite-structured phases and their high-pressure polymorphs called post-spinel and post-perovskite phases. The last part of the book focuses on phase relations of mantle rocks and on natural high-pressure minerals from the Earth’s deep mantle and in shocked meteorites.