In the book, from a wide range of problems and tasks, questions are selected, acquaintance with which represents the necessary element of education of a scientist - a theorist or experimenter interested in any branch of condensed matter physics. The concept of collective excitations is introduced - quasiparticles as a means of analyzing weakly excited states of condensed media. Methods of theoretical description of periodic structure of crystals and behavior of electrons in crystalline solids are considered.