The textbook analyzes the psychological mechanisms of the functioning of concepts as structural units of the mental activity of individuals. Theoretical approaches to studying the content characteristics of concepts as tools of thinking are described. Diagnostic means for detection of level of development of conceptual structures are presented. The textbook was developed as part of the training program - an academic master's degree in psychology, a training course "Actual problems of the theory and practice of modern psychology." Applicable to students and undergraduates studying general psychology, history of psychology.