This book on Quantum Mechanics starts with the known field equation of Electrodynamics. Then comes the following steps: in the case of very weak fields the electromagnetic field equation becomes the quantum mechanical wave equation for single photons. This equation is generalized for massive particles (Klein-Gordon equation). The non-relativistic limit of this is the free Schrödinger equations. In this way the correspondence rules (leading from the Hamilton function to the Hamilton operator) are motivated.On the whole, this book concentrates on applications, and on how things can be calculated . The formal structures are treated to the necessary extent.The applications include all standard topics (including alpha-decay, the hydrogen atom including relativistic correction, angular moment coupling, the Stark effect) and proceed to many-body problems. This includes an introduction of the shell model of the atom and that of the atomic nucleus.