Of the three branches of government traditionally distinguished since Montesquieu, two have received ample scholarly attention in their relation with the European Union. A plethora of books and articles have been written on the role and position of national courts and national parliaments in Europe. As to the former, the interaction of national courts with the Court of Justice of the European Union is still massively researched. As to the latter, it has been thoroughly analysed how national parliaments were sidelined from the start of the integration process, only to regain lost ground later. In particular, attempts to include the national parliaments in EU decision-making, via the renewed Subsidiarity Protocol among other ways, have attracted numerous research activities.