The first textbook in the CIS on psychological diagnostics was written by one of the famous and leading not only today, but also in pre-perestroika time specialists in this field. The book examines in detail the history, subject and methods of this most important branch of psychological knowledge. Questions related to the mathematical and statistical substantiation of the measurement of individual differences and the construction of psychological tests. are presented. A significant place is given to both theoretical and practical problems of measuring (testing) intelligence and personal characteristics. The textbook is intended for students of higher educational institutions studying in the specialty "Psychology", graduate students, as well as specialists solving diagnostic tasks in their daily activities.