The book summarizes the author's experimental studies of phase relations in the chemical systems relevant to earth, carried out in a time period of over 20 years using piston-cylinder and multi-avil presses. A summary of the research at high pressures and temperatures carried out by many other experimental petrologists is also included. The data was used to develop an internally consistent thermodynamic model, which was then used to calculate phase diagrams. This produced the largest collection of the calculated phase diagrams published to date and the first to encompass temperature and pressure ranges corresponding to the whole upper mantle.