Based on a university course, this book provides an exposition of a large spectrum of geological, geochemical and geophysical problems that are amenable to thermodynamic analysis. It also includes selected problems in planetary sciences, relationships between thermodynamics and microscopic properties, particle size effects, methods of approximation of thermodynamic properties of minerals, and some kinetic ramifications of entropy production. The textbook will enable graduate students and researchers alike to develop an appreciation of the fundamental principles of thermodynamics, and their wide ranging applications to natural processes and systems.