The textbook is devoted to elementary thinking, or rational activity - the most complex form of animal behavior. For the first time, the reader is offered a synthesis of classical works and the latest data in this area, obtained by zoopsychologists, physiologists of higher nervous activity and ethologists. The manual reflected the content of lecture courses that authors have been reading for many years at Moscow State University. M.V. Lomonosov and other universities. An extensive list of references is intended for those wishing to independently continue acquaintance with the problem.