This monograph investigates the properties of crystal, liquid and gas phases of substances, and also metastable states. New relations for the thermodynamic similarity for liquid-vapour phase transitions are derived, and the authors describe solid-liquid, liquid-vapour and liquid-liquid phase transitions for binary systems employing the methodology of thermodynamic similarity. Prof. Skripov received acknowledgement worldwide through his monograph on metastable liquids, published by Wiley & Sons. For over fifty years now he has been working in the field of thermodynamics of liquids and vapours, wherein he is an outstanding expert.