The main idea of the book is to give a correct understanding of the physical foundations of quantum mechanics, its mathematical apparatus and show the ways of its application in various fields of physics. Additions and changes have been made to previous editions, taking into account the development of the theory. The presentation of the theory of measurements in the quantum field has been significantly expanded and deepened. The form of causality in quantum mechanics is covered in more detail. Expanded description of diffraction scattering and optical model of particles. The concept of the analytical properties of the scattering matrix and the poles of the Regge. Feynman's formulation of quantum mechanics, using integration along trajectories. The simplest problem of nonlinear optics is considered. The book has been published many times in many countries and remains popular in our time. For physics students and researchers .