The notion of “improper co-authorship” is not known to the criminal law of the Republic of Moldova. This notion is part of a broader notion – “improper participation” – which is used in Romanian criminal law. The last notion is based on the theory of improper participation, which was developed by Romanian doctrinaires. The theory of improper participation is characterized by the fact that some participants act intentionally, while others act by imprudence or without guilt. The arguments presented in this investigation confirm that, in the context of the criminal law of the Republic of Moldova, the theory of improper participation is complementary to the theory of the mediated author. Improper co-authorship in the manner “intent – lack of guilt” is found in the aggravating circumstance of “two or more persons”, recorded in the special part of the Criminal Code of the Republic of Moldova, if the act, provided by criminal law, is committed by two direct perpetrators – one of whom is criminally liable and the other is not.