As the title of the Special Issue suggests, its main purpose is to shed new light on the content, scope, extent, and limits of Article 267 TFEU in today’s Union and, in turn, on the nature of this procedure and the European Court of Justice (ECJ)’s role as a sui generis supranational court. Such role has been played first and foremost through the rulings rendered in the context of the preliminary ruling procedure, which has been defined as the ‘keystone’ of the EU judicial system,2 the ‘most important aspect of the work of the Court’,3 the ‘jewel in the Crown’ of the Court’s jurisdiction,4 and the ‘genius’ without which core principles, such as direct effect and primacy, could have not been conceived.5 Indeed, the procedure enshrined in Article 267 TFEU has shaped and continues to shape profoundly the EU legal order and the relationship between the EU and the Member States.Moreover, this procedure shall not be seen simply as a tool used by the Court of Luxembourg to strengthen the evolution of EU law. In fact, the way Article 267 TFEU has been constantly interpreted, redesigned, and materially reformed over the decades is also a symptom of the dynamics underpinning such evolution. This transformative and mimetic nature of Article 267 TFEU explains the evergreen interest in the procedure despite the absence of any amendment to the Treaties since the 1950s, confirmed by the large number of studies published on the subject over the last few years.