Almost one quarter of the aquis communautaire is made up of directives; European regulation that specifies policy objectives, but leaves the regularity implementation up to the Member States. 1.6% of European directives are not or insufficiently transposed into national law, impairing the functioning of the single market and, ultimately, the principle of legal certainty. Also, the quality of implementation varies significantly among the Member States. The Better Regulation Strategy should aim at improving both the level and quality of transposition in the Member States.
The respective wiki article that is referred to is found here.