The task of monitoring the application of Community law falls to the European Commission as the guardian of the Treaties. It is an expression of the fact that the European Union is based on the rule of law and its purpose is to make sure that the law is observed and actually applied in and by the Member States. In exercising its monitoring function the Commission takes care to safeguard the role which is also assigned to national authorities, particularly the courts, in this area.
Monitoring the application of the law may take the following forms:
instituting infringement proceedings following complaints or where cases are discovered in the ordinary course of events;
court action against the other institutions;
checking whether aid given by the Member States is lawful;
checking that the principles prohibiting certain types of agreements, decisions and concerted practices and the abuse of a dominant position are observed.
The Commission's annual reports on the application of Community law are an expression of the desire for transparency in dealings not only with complainants but also with citizens and members of parliament.
See:
Citizenship of the Union
Court of Justice of the European Union
European Commission
Transparency (access to documents)