The new edition of the book is mainly a course of lectures on quantum mechanics, read by the author for a number of years at the physical faculty of Moscow State University named after M.. In. Lomonosov . The natural development of this course of lectures prompted the author to make a number of changes and additions to the second edition. A significant change was made to the chapter relating to the concept of state in quantum mechanics and to the discussion of the uncertainty relationship, where greater clarity has been introduced. The new edition of the book examines and criticizes the idealistic concepts of quantum theory that are now common abroad. In addition, additional additions have been made due to the further development of quantum mechanics applications in recent years. In this book, the author sought to give the beginner to study quantum mechanics the correct understanding of its physical foundations, its mathematical apparatus, to show on the most important applications the fruitfulness of this science.