This book summarizes the results of the experimental studies of phase relations in the chemical systems relevant to Earth, carried out by the author in a time - riod of over 20 years between 1979 and 2001.It is based on 1000 piston-cylinder experiments at pressures up to 4 GPa, and close to 700 experiments carried out with a multi-anvil apparatus at pressures up to 24 GPa.The emphasis in these studies was on internal consistency.Large sets of data were produced using the same sample assembly, high-pressure apparatus, experimental procedures and calibrations by the same experimentalist to maximize the internal consistency. The results were published in 69 peer-reviewed articles listed at the end of the book.These are referenced only by the corresponding number, while the full r- erence is given for all other sources. The need for a summary, possibly in the form of a book, had become evident early on in the course of these studies, since it was impossible to publish int- mediate results of separate research projects within the framework of an int- nally consistent thermodynamic model, while the work was still in progress.