This book provides a lucid introduction to the basic ideas of quantum mechanics.Meant for undergraduate and graduate physics students, it contains discussions on advanced topics that will be beneficial for researchers also.The text is designed according to the syllabi followed in major Indian universities.Chapters are designed to provide an equal emphasis to physical as well as mathematical significance of concepts.The text is divided in four parts. The first part introduces concepts of formalism and includes topics, namely wave-particle duality, state vectors, and symmetry.The second part comprises discussions on exactly solvable problems.This is followed by the third part which deals with various approximation techniques including degenerate and non-degenerate perturbation theory, WKB approximation, and Born approximation.The fourth part of this book deals with advanced topics like permutation symmetry, Dirac particle in a central potential, and EPR paradox.