The purpose of this book is to provide an overview of important principles and concepts in the field of thermodynamics,written in a fashion that makes this abstract and complex subject easy to comprehend. Intended to serve the needs and interests of energy-involved engineers, the content, concepts and principles are presented in a way which also will allow many non-engineering professionals with some math background to follow the material and gain useful knowledge. Thermodynamic topics including enthalpy, entropy, latent and sensible heat, heats of fusion, and heat of sublimation are clearly presented. Also covered are phases of substances, the law of conservation of energy, SFEE, the first and second laws of thermodynamics, ideal gas law, and respective mathematical statements.