Written by two researchers and teachers, this text offers a presentation of the foundations and applications of thermodynamics. This textbook is arranged around a variety of topics which make it suitable for several distinct courses at different levels. The author attempt to achieve clarity and logical consistency without employing abstract formalisms and ad-hoc, ambiguous and incomplete definitions. Every effort is made to motivate the reader with examples from everyday engineering experience. Concepts are introduced in a logical sequence, eliminating the problem of incomplete, misleading, of ambiguous definitions. The laws of thermodynamics are stated in a generalized manner, and as fundamental laws of physics which complement the laws of dynamics. Without modifying the basic concepts, all principles and results are applied to microscopic and macroscopic systems, and to non-equilibrium and equilibrium states. End of chapter problems test students understanding of the chapter concepts, as well as the cumulative material.