Translator N. Lisova . Along with the traditional material covered by the course of quantum mechanics (states, operators, Schrdinger equation, hydrogen atom), the book offers an in-depth discussion of concepts such as Hilbert space, quantum measurement, entanglement, and decoherence. These concepts are crucial to understanding quantum physics and its relationship to the macroscopic world, but are rarely addressed in entry-level textbooks. The book uses a mathematically simple physical systemphoton polarizationas a visualization tool, allowing the student to see the intricate beauty of the quantum world from the very first pages. The formal concepts of quantum physics are illustrated by examples from modern experimental studies, such as quantum computers, communications, teleportation, and nonlocality. The material of the book has been successfully used as a basic teaching aid in a two-semester course in quantum mechanics for physics students. However, the potential readership is much wider and covers both students and graduate students studying the exact sciences, as well as all those interested in quantum physics and quantum technologies. The mathematical apparatus required to understand the book does not go beyond the course of a technical university or a mathematical school. The author, a professor at the University of Oxford and a world-renowned experimenter in quantum optics and quantum computer science, applies Socratic pedagogy. The student is invited to independently develop the apparatus of quantum physics by sequentially solving carefully compiled problems. Detailed solutions are presented in the second volume of the manual.