Over the years, many theories have tried to explain the puzzle of cross-national variation in preliminary reference rates before the ECJ. Most of the contributions focused on the role of national judges, examining their legal education, policy preferences, workload, and attitude towards higher courts. This article adopts, instead, a legal mobilization perspective that decentralizes the role of courts and redirects the focus to the litigants and their political context. Relying on empirical research and on a comparison of three country case studies in the field of migration, the article argues that national patterns of mobilization influence the emergence of preliminary references. Moreover, it identifies three factors at the national level that help understand when legal mobilization occurs via preliminary reference: altruism, Euro-expertise, and EU legal opportunity structure. The article makes both an empirical and a theoretical contribution by bridging the scholarship on legal mobilization and EU judicial politics.