Criminal matters remain a sensitive policy area. In spite of the link with national identity and sovereignty, the EUs competence in ‘criminal matters’ has steadily grown over the past decades. The substantive scope of the competence is widened, decision making amended and the role of the CJEU gradually recognised. Strikingly, the concept of ‘criminal matters’ was never defined at EU level. For long the interpretation thereof was left to the member states. Only recently the role of the CJEU was recognised, opening the door for the CJEU to use its plethora of interpretative methods to define the concept. Unfortunately, the CJEUs interpretative methods are not transparent and not adjusted to criminal matters. Some methods used are irreconcilable with fundamental principles underpinning the EUs competence in criminal matters. This project seeks to develop a new interpretative framework for the CJEU to use specifically for criminal matters. Firstly, the current knowledge on the interpretative methods of the CJEU will be updated as existing research is rather old. Secondly, the different interpretative methods will be applied to a selection of legal instruments to be able to get insights into the functioning thereof. This has never been done before. Thirdly, the compatibility of those interpretations will be tested against the constitutional framework of a selection of member states. These three steps will allow the researcher to construct a new interpretative framework.