The implementation of EU law is articulated in a plurality of levels. Article 291 TFEU confers the primary responsibility of implementing EU law on the Member States, but it envisages also a direct implementation at the EU level where uniform conditions are required. However, the reality is more complex than the image enshrined in Article 291 TFEU. At the EU level, the implementation is carried out not only by the Commission and the Council in duly specific cases, but also by bodies not expressly envisaged in Article 291 TFEU, such as EU agencies and private standardisation bodies. The accountability mechanisms for the exercise of such implementing powers are considerably different and, for certain aspects, problematic. The contribution, therefore, analyses the different forms of implementation which have emerged in EU law and it will compare the mechanisms in place, shedding light on some blind spots in the democratic control and in the judicial review of these phenomena.