Thermodynamics is a branch of physics associated with heat and temperature and their relation to energy and work. It defines macroscopic variables, such as internal energy, entropy and pressure that partly pronounce a body of matter or radiation. It mentions that the behaviour of those variables is subject to general constraints that are common to all materials, not the peculiar properties of particular materials. These general constraints are expressed in the four laws of thermodynamics. Thermodynamics describes the bulk behaviour of the body, not the microscopic behaviours of the very large numbers of its microscopic constituents, such as molecules. Thermodynamics applies to a wide variety of topics in science and engineering, especially physical chemistry, chemical engineering and mechanical engineering. Initially, thermodynamics, as applied to heat engines, was concerned with the thermal properties of their working materials, such as steam, in an effort to increase the efficiency and power output engines. Thermodynamics was later expanded to the study of energy transfers in chemical processes, such as the investigation of the heats of chemical reactions, which was not originally explicitly concerned with the relation between energy exchanges by heat and work. From this the study of chemical thermodynamics and the role of entropy in chemical reactions are evolved. Engineering Thermodynamics is characterised by exhaustive study of topics such as thermodynamic applications, powerplant engineering, refrigeration and automobile IC systems. The book highlights the various thermodynamics concepts such as temperature and gas laws, work and heat transfer, entropy, energy and its reversibility, and properties and mixtures. The book also focuses the principles, concepts, and laws/postulates of classical and statistical thermodynamics to applications that require quantitative knowledge of thermodynamic properties from a macroscopic to a molecular level. The book follows a comprehensive approach such that engineering students, working professionals, and research associate can benefit from the book.