This book provides important and relevant theories in quantum mechanics. Human understanding regarding the universe and nature driven forces have been thoroughly influenced by the Quantum theory as a scientific revolution. Possibly, the historical advancement of this concept mimics the history of human scientific endeavors from their birth. The book presents a valuable account of foundation, scientific history of the concept, distinct techniques to solve the Schrodinger equation, and relativistic quantum mechanics and field theory. Some of the important topics are complementarity in quantum mechanics & classical statistical mechanics, and theory of elementary particles based on Newtonian mechanics. The aim of this book is to serve as an efficient reference for researchers and students.