Each principle of law exists on three levels: a legal doctrine, a normative text and a legal practice. Thus the existence of a principle is much broader than its legislative level. However, the functioning of the principle in the legal system is impossible without its legislative fastening. This fastening can be indirect (through the other norms) or direct. In this case a principle looks like a legal rule. But they are quite different. The difference between legal rules and principles attracts the attention of both foreign and Russian researchers. In English-language books the “norm” as a generic term includes the “rules” and “principles”. In the Russian legal language “norm” and “rule” are used as the same word. Therefore, some scholars use the terms “norm-rule” and “norm-principle” which sound tautological. Others use the term “normative legal prescription” as a generic one. As separate groups of prescriptions the principles and rules differ from each other by substantive, formal and functional features. The normative level does not provide an exhaustive knowledge of the legal principles, but contributes to their abstract character. We can examine technical and legal side of the legal principles, their structure, and understand their relationship with other legal phenomena (axioms, presumptions and so forth). As a result, it becomes possible to make the process of direct implementation of the legal principles more understandable for the law enforcer.