The author of the famous course of quantum mechanics devotes this monograph to the fundamental questions of quantum mechanics, which are fundamental to understanding this important theory. The author pays special attention to the analysis of the relationship of the microsystem with the macro-environment surrounding it, in particular, to the analysis of the operation of the macroscopic device. The concept of the author is not generally accepted and well-known, and this makes the book especially interesting. The book is intended for a wide range of physicists, theorists and experimenters interested in the basics of modern theory. It will also be useful and interesting for philosophers involved in the methodology of modern natural science.