The European Court of Justice plays a key role in the interpretation and enforcement of EU law. Yet, we still know little about the conditions under which cases arrive at the Court via preliminary reference and why they are so unevenly distributed across the EU Member States. Previous studies have shown how the legal elites played a central role in feeding the Court with cases to increase their power and influence. _Legal Mobilization for Migrant Rights_ tells a different story. Focusing on the migration domain, this book shows that EU litigation can also be used to defend powerless groups. To explore the conditions under which EU legal mobilization for migrants emerges, the author compares three countries where EU migration law was mobilized before the European Court of Justice (Italy, the UK, and the Netherlands) and one where it was not (Greece). Combining empirical and doctrinal methods, this volume draws on interviews with key stakeholders and an original database of 505 migration preliminary references. Rather than focusing only on courts, _Legal Mobilization for Migrant Rights_ sheds light on the role of lawyers, academics, and civil society in activating EU justice to oppose restrictive national migration policies. Crucially, the book ultimately reveals that EU legal mobilization struggles to emerge in some contexts due to a lack of resources and limited awareness of EU legal opportunities, which stand as significant obstacles to justice and migrant rights enforcement.