Data on the polymorphic phase transformations of known compounds and new synthetic compounds of the type AB2have been compiled and evaluated. All available pressure studies have been included and referenced. Pressure‐temperature phase diagrams showing first order solid‐solid phase boundaries and/or melting curves showing the best fit to the experimental data are included. For some materials which can be produced only by chemical synthesis techniques at high pressures and high temperatures, reaction‐product diagrams have been employed to estimate the region of thermodynamic stability. Crystallographic data of all the known phases of each material have been tabulated and evaluated. This review covers 168 compounds and 332 phases including the room temperature atmospheric pressure phase for each compound when it exists.