This book is designed to meet the requirements of undergraduate students. Realizing the mental state of students every attempt has been made to present the material in most elementary and easily digestible form. Salient Features: The book has been divided in two parts. The first part deals with kinetic theory of gases, transport phenomena, equations of state, laws of thermodynamics, entropy, production of low temperature, conduction of heat and radiation. All equations and thermodynamic relations have been expressed in terms of specific values of extensive variables and these variables have been denoted by lower case letters (v, u, s). The intensive variables have been denoted by upper case letters (P, T). A large number of solved examples have been provided to make the audience feel confident in applying the principles of thermodynamics to various phenomena. The second part of the book deals with the development of concepts of statistical mechanics. Chapter 1 begins with the development of concepts of macrostate, microstate, quantum state, density of state and statistical weight. Chapter 2 develops the concept of phase space, mu-space and gamma-space. Chapter 3 discusses the concept of ensemble and the fundamental principles of statistical mechanics. A brief introduction of thermodynamic functions is given in Chapter 4. The well-known distribution functions M-B, B-E and F-D are discussed in Chapter 5. The application of these distribution functions have been given in Chapter 6. Chapter 7 presents partition function and its application to specific heat problem is discussed in last Chapter. Table of Contents Part-1: Thermal Physics Kinetic Theory of Gases Transport Phenomena Equation of State for Gases Zeroth Law of Thermodynamics : Preliminary Concepts First Law of Thermodynamics Heat Engines and Second Law of Thermodynamics Entropy Thermodynamic Relations Production of Low Temperature and Liquefaction of Gases Conduction of Heat Thermal Radiation Part-2: Statistical Physics Preliminary Concepts Phase Space Ensemble Formulation of Statistical Mechanics Thermodynamic Functions Distribution Laws Applications of Quantum Statistics Partition Function Applications of Partition Function