3rd stage is a course of lectures on game theory and is intended for chess players who want to improve their qualifications. The book consists of two parts, each of which contains 15 lessons. A large place in it is given to exercises for independent work, developing and consolidating the knowledge gained. At the end of each part, answers to tasks are placed. The heading "chess yesterday," today, tomorrow introduces the centuries-old history of chess. The book Chess ABC, stage 3 also included historical chronicles and excerpts from works of art dedicated to the unfading game.