Quantum Mechanics is a fascinating branch of science that deals with the nature of the universe at a nanoscopic level. It describes how all particles in the universe behave at the smallest scale. It explains how all natural phenomena of classical physics originate. The book deals with almost all major quantum theories and their derivatives, Quantum Field Theory, and the String Theory. Through various experiments, the book explains the core of Quantum Mechanics qualitatively. Besides describing Quantum Mechanics, the book describes the fundamentals of the Theory of Relativity and how the idea of Quantum Gravity was formalized.