"Quantum Mechanics" describes the phenomena that matter and light exhibit on an atomic scale and so the study of atomic physics, nuclear physics and solid state physics are impossible without a clear understanding of the basic concepts and formalism of "Quantum Mechanics". Since Physics deals essentially with numbers - the measurement of physical quantities and the calculations of these quantities on the basis of a theoretical framework - adequate attention has been paid to computation and numerical exercises. This book aims to promote a comprehensive understanding of the subject with illustrative examples. New to the second edition: Four appendices F, G, H and I. The appendices F, G and H are the elaboration of the mathematical tools - Dirac delta function, angular momentum in spherical coordinates and orthogonal curvilinear coordinates - that are used in the text. The appendix I on symmetry principles and conservation laws is an important and vital part of physics since almost all laws of nature originate from symmetries.