This slim volume covers the traditional parts of quantum mechanics: semiclassical theories of radiation and scattering, a number of advanced problems: Feynman diagrams and relativistic quantum mechanics and a collection of modern items: superfluidity and high-temperature superconductivity. The book begins with the description of the basic principles of mechanics, electrodynamics and quantum mechanics, which are needed for understanding the subsequent chapters. Qualitative methods (analytical properties and paradoxes in quantum mechanics) are also introduced. This useful textbook also pairs the problems with their solutions.