Much research has been undertaken to cast light on to the role of interest groups in the European Union and elsewhere. However, only a few researchers have focused their energy on the practical effects of involvement – effects on the legal output of the political process. Thus, we have a good knowledge of interest groups as input factors and we have a language to asses their weight in terms of input legitimacy. However, we do not understand their actual impact on the substance of legislation: does involvement make laws more efficient? This question seems especially relevant in the EU as this organisation is often said to be much dependent on the effective and efficient functioning of its rules – its output legitimacy.