The text systematically employs the basic language of set theory. This approach is often useful for solving combinatorial problems, especially problems where one has to identify some objects, and significantly reduces the number of the students’ errors; it is demonstrated in the text on many examples. The textbook is suitable for undergraduate and entry-level graduate students of mathematics and computer science, lecturers in these fields, and anyone studying combinatorial methods and graphical models for solving various problems. The book contains more than 700 problems and can be used as a reading and problem book for an independent study seminar or self-education.