The paper presents the issues of cooperation in criminal matters analysed in the context of the process of Europeanisation. In the Polish legal system, the process mainly results in the development and implementation of new and varied forms of cooperation in criminal matters with the European Union Member States. The mechanisms of cooperation transposed to the Criminal Procedure Code are, in fact, nothing new for the current model of proceedings developed in accordance with the Code of 1997, because it envisaged most of the already operating forms of international cooperation. The institutions of cooperation, although already regulated on the basis of Polish law, lacked some important basic features and were mainly based on political decisions of the executive power. That was the reason for the necessity of implementing the EU models increasing the framework of cooperation in criminal matters by gradually making the regulations more specific and elaborate. This, as a result, has led to the development of a new, complex and at the same time inconsistent system of cooperation with Member States. [PAR] The creation of a completely composite regulation within Section XIII CPC, about which it is difficult to speak in terms of the system coherence, was a side effect of the implementation of provisions concerning the development of cooperation in criminal matters. The removal of the regulation of Section XIII from the Criminal Procedure Code and enacting it as a separate legal act may be a remedy for the present situation.