Continued advances in thermodynamic models of mineral and fluid equilibrium and in the kinetics of mineral reactions have made metamorphic petrology a quantitative science. Thermometers and barometers for many rocks are accurate enough to locate the origin of the rocks in the crust and mantle, and the development of kinetic models promises to enable tracing the P‐T path through time of individual specimens of some rocks. Data on the flow of fluids through metamorphic rocks and their interaction with minerals contributes toward an understanding of the processes responsible for the formation of some ore deposits and the geochemical evolution of the oceans. Models of partial melting should prove to be useful for predicting igneous contamination.