This textbook has been specifically developed on the directives of National Education Policy (NEP 2020) and is as per latest curriculum of B. Sc. Physics (Fifth Semester) for the Universities of Uttar Pradesh. This book comprises of two parts: Part A and Part B. Part A deals with the Introduction of Classical Mechanics. This begins with Constrained Motion followed by Lagrangian Formalism, Hamiltonian Formalism and Motion under Central forces. Part B on Introduction of Statistical Mechanics starts with Macrostate and Microstate followed by Concept of Ensemble, Three Statistical Distribution Laws namely Maxwell-Boltzmann Statistics, Bose-Einstein Statistics and Fermi-Dirac Statistics. Their applications are lucidly explained at the end of the book.