Statistical mechanics is one of the fundamental papers for MSc Physics and MSc Chemistry courses and this title can be used as a textbook for these courses. The topicsThermodynamics, Microcanonical ensemble, Canonical ensemble, Grand canonical ensemble, Maxwell-Boltzmann distribution, Fermi-Dirac distribution, Bose-Einstein distribution for an ideal gas are discussed in a systematic manner by using simple language. The discussion is extended to account for interaction among the constituent particles of a real gas and the phase transitions for a matter. Finally, the kinetic and dynamical theories of gases are discussed. Each of the topics is developed in a systematic manner and is supported by exercises.