Thermodynamics is a branch of natural science concerned with heat and its relation to energy and work. It defines macroscopic variables (such as temperature, internal energy, entropy, and pressure) that characterize materials and radiation, and explains how they are related and by what laws they change with time. Thermodynamics describes the average behaviour of very large numbers of microscopic constituents, and its laws can be derived from statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering-such as engines, phase transitions, chemical reactions, transport phenomena, and even black holes. Results of thermodynamic calculations are essential for other fields of physics and for chemistry, chemical engineering, aerospace engineering, mechanical engineering, cell biology, biomedical engineering, and materials science-and useful in other fields such as economics. Much of the empirical content of thermodynamics is contained in the four laws. We shall therefore consider labours amply rewarded if the book receives warm reception and appreciation from the teachers and the taught. Though nothing can be claimed as original but the subject matter has been arranged in my own style. Suggestion for improvement of the book will be gratefully acknowledged.