This working paper is part of the Court of Justice in the Archives project, shedding new light on a seminal case in the jurisprudence on free movement of workers in the European Union: Case 147/97, Commission v Belgium. The paper reports findings from accessing and analysing the digitalised original case files from a perspective focusing on how the archival resource could contribute to socio-legal research. From this particular case-study, two key takeaways emerged. First, the case-files were a valuable asset to reconstruct the social and political context of the decision, spanning the period from the petition to the final judgment. Whilst the parties’ submissions contained good indications, consulting additional secondary sources proved necessary to flesh out the connections between the context and the content of the submissions. Second, with regard to actors, institutions and procedure, the casefiles proved a powerful resource to gain insight into the pre-litigative infringement procedure. Whilst a single case-study does not suffice, using the archival resources with comparative methods seems a promising avenue for conducting socio-legal research into the machinery, procedural culture and social dynamics at the Court and other institutions in the past to inform our understandings of the present.