The monograph examines in detail modern portfolio theory, which was developed by G. Markowitz, supplemented by W. Sharp and others. Using the methods of higher mathematics and probability theory, a critical analysis of the main provisions of portfolio theory is carried out. Modern principles, approaches and methods for evaluating securities are analyzed. The specific features of strategic management of investments in securities are described. An alternative approach is proposed for comparing securities and forming an optimal portfolio of assets. A mathematical apparatus for evaluating standard options has been developed. The book is recommended as a textbook for students of economic universities, graduate students, teachers and as a methodological guide for stock market participants.