The Treaty of Lisbon opened the door for the inclusion of subnational parliaments in the EU decision-making processes. However, authors have so far mainly focused on the involvement of national parliaments and only rarely included both regional and national parliaments in one single analysis. Consequently, we know little or none about the variation and, more interestingly, the relationship between multiple parliaments from different levels of governance within a Member State. However, if one wants to study the role of parliaments from federal Member States in EU decision-making processes, it is crucial to examine the combined actions and relations among regional and federal parliaments regarding EU affairs. This paper therefore examines, in a comparative perspective, the politicisation of EU affairs within the Belgian House of Representatives, and the parliaments of Flanders and Wallonia (sample of the legislative period 2009-2014). This version presents the first descriptive findings of manually coded parliamentary debates. It looks at which parties and members of parliaments participate in EU-related debates, and at the policy field and type of EU dossier under scrutiny. In a next stage, we aim at explaining variation in EU politicisation within Belgium, and what this means for inter-parliamentary relations within Belgium.