Statistics of the European Commission show different performances among member states regarding the implementation of European policies. In particular, this article explains why Denmark and Belgium have different records with respect to the legal or administrative transposition of European Union environmental directives. The article starts with a short overview of the implementation problematique and a presentation of the latest available statistics. Then European-level factors are ruled out as possible explanations for the differences in performance. The author argues, on the contrary, that the differences between Belgium and Denmark must be explained by national institutional contexts. To this end, an institutional approach is presented, which draws attention to ‘hard’ and ‘soft’ institutions as explanatory variables. In total seven categories of variables are discussed: four ‘hard’ categories – the constitutional and administrative context (division of competencies and coordination mechanisms), institutional capacity, administrative and legal adaptation pressure, communication and continuity – and three ‘soft’ categories – institutional jealousy, Europeanisation and political adaptation pressure. It was found that both member states under study have different scores on almost all variables, pointing to rather unfavourable implementation conditions for Belgium and much more favourable conditions for Denmark.