Now it's obvious that quantum physics enters within the twenty-first century into a chiefly new and vital part of its development which can cardinally amendment the presently used technical facilities within the areas of data and telecommunication technologies, precise measurements, medication etc. Indisputably, all this on the whole will change the production potential of human civilization and influence its morality. The central question which arises on the way of gaining a deeper insight into the quantum nature of various phenomena is the establishment of well-known accepted criteria of applicability of quantum mechanics. In order to answer this essentially important question for development of quantum physics, it is necessary to expand substantially the concepts upon which quantum mechanics is based. This book presents a solid understanding of the fundamental concepts and results of quantum mechanics as well as the historical background and philosophical questions. It highlights different applications of quantum mechanics in the field of science and technology. The book opens with the concepts of classical or quantum, what is reality? The book further probes the question of what interpretations of quantum mechanics actually accomplish. Interpreting quantum mechanics has flourished as a cottage industry among philosophers of science and some philosophically inclined physicists. Physicists regularly ignore, and sometimes ridicule, such attempts. Interpretations of quantum field theory are polarized by the divergence between the Lagrangian field theory, which leads to the Standard Model of Particle physics and the Algebraic quantum field theory that discounts ontology of particles. Ruetsche’s interpretation offers a potential for loosening the sharp polarization that presently obtains. A brief evaluation focuses on the functional ontology of quantum field theory considered as an effective theory. Moreover, the book sheds light on the statistical origins of quantum mechanics. It is shown that Schrödinger's equation may be derived from three postulates. The first is a kind of statistical metamorphosis of classical mechanics, a set of two relations which are obtained from the canonical equations of particle mechanics by replacing all observables by statistical averages. The second is a local conservation law of probability with a probability current which takes the form of a gradient. The third is a principle of maximal disorder as realized by the requirement of minimal Fisher information. Now, the book goes on to non-commutative quantum mechanics in time - dependent backgrounds and the origin of momentum operator. Finally, the book includes a general scheme of constructing the nonrelativistic quantum mechanics of a bound system with FE. In the second part of the chapter we consider the problem of a quantum harmonic oscillator with fundamental environment. Since this model is being solved exactly, its investigation gives us a lot of new and extremely important information on the properties of real quantum systems, which in turn gives a deeper insight into the nature of quantum foundations. In the final chapter, we present recent advances of theoretical analyses toward understandings of functional mechanisms of biological macromolecular systems, employing ab initio electronic structure calculations. In order to understand the mechanisms of biological functions, analyses of the electronic structure changes for the catalytic reactions are essential. This book will appeal to scientists and researchers, as well as students, conversant with the fundamentals of quantum mechanics.