The course is designed to give the students a firm understanding of statistical mechanics at the advanced undergraduate/beginning graduate level. After a discussion of the concepts of probability, the postulates of classical mechanics are developed in various ensembles of physical relevance. The ideas thus developed for the classical systems will be shown to have serious limitations when applied to quantum systems. Finally, we develop the correct theory of statistical mechanics for quantum systems and show that classical results can be recovered from the quantum theories in the high temperature - low density limit. (from nptel.ac.in)