The most pressing issues necessary for understanding the factor of complexity in the legal system, which are insufficiently represented in educational literature, are covered. At the same time, the theoretical aspects of the relationship between the legal system and the legislative system are clarified, the legal nature and types of complex legal entities are analyzed. Attention is paid to the characteristics of the complex as a specific system, the division of law into private, public and social. The book is intended for masters, researchers, lawyers, graduate students, teachers of law schools. It will also be of interest to all students of the theory of state and law.