The formal source of criminal law should be recognized as those legal acts that can be directly applied by courts in resolving criminal cases and to which the court must directly refer in a court decision to justify its decision. The criminal law doctrine has convincingly proven the multi-source nature of the branch of criminal law. At the same time, the modern doctrine of sources sorely lacks a differentiated approach to their analysis and presentation. The implementation of a systematic approach in the context of a general theoretical doctrine of the forms of expression of law allows us to identify several substantively divergent groups among the sources of criminal law: a) sources of regulation of criminal legal relations that do not contain criminal legal regulations; b) sources establishing criminal legal regulations, including the criminal code as the only source establishing crime and punishability of socially dangerous acts; c) sources of normative specification of criminal legal regulations; d) sources of interpretation of criminal law regulations. Keywords: source of criminal law, systematic approach, source of establishing an order, source of specifying an order, source of interpretation of an order.