Cooperation between authorities conducting administrative investigations and those conducting criminal investigations at both the EU and Member State levels is essential to ensure a high level of protection in view of the EU's financial interests. However, the legal framework governing the role and competences of individual authorities at the EU level seems much clearer than the corresponding national legal frameworks of the Member States. Indeed, at the Member State level, the legal frameworks for conducting investigations, whether administrative or criminal, significantly differ from Member State to Member State. Likewise, there is no clear legal framework at the EU level that defines and sets standards regarding the mandatory control mechanisms that must be established at the level of the entire system for the protection of the EU’s financial interests in the Member States. This also applies in relation to the players that need to be involved in the protection of the EU's financial interests. The article tackles the issue of the necessity to harmonise both criminal and administrative legislation at the level of Member States as well as the need for a clear definition of which players should be involved in the protection of the EU budget.