The essence and contents of the modern theory of sources of law within the national legal doctrine in the context of integrative the right of understanding is investigated. The analysis of evolution of the theory of sources of law within the separate historical periods is carried out, their concept, the main signs and properties, a ratio decides on such categories as a legal form and a form it is right. Classification of sources of law, in particular in legalistic sense is carried out, their functions and tendencies of further development are defined. The system of sources of law, its properties, communication between separate sources is separately characterized. It is noted that the theory of sources of law has the conceptual and categorical device and according to classification looks so: normative legal act, law-making treaty, legal precedent, legal custom, legal doctrine, general principles of the right. Besides, the contents of the theory of sources of law are formed by knowledge gained as a result of definition of methodology of a research of sources of law, their analysis in the light of concepts the right of understanding and clarification of functions of sources of law