Quantum mechanics is a theory in physics that explains the physical properties of nature at the atomic and subatomic levels. It is fundamental to the study of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science. Classical physics defines many aspects of nature at an ordinary scale, while quantum mechanics describes the aspects of nature at small scales. Most theories in classical physics can be derived from quantum mechanics as an estimation valid at large scale. Quantum mechanics is used to describe observations which could not be resolved with classical physics. This book attempts to understand the multiple branches that fall under this discipline and how such concepts have practical applications. Different approaches, evaluations, methodologies and advanced studies on quantum mechanics have been included herein. The extensive content of this book provides the readers with a thorough understanding of the subject.