The preliminary reference procedure in Article 267 of the Treaty on the Functioning of the European Union (TFEU), which enables national courts to request the Court of Justice to provide a ruling on the interpretation or validity of an EU legal act, is widely considered to be the jewel in the crown of EU law. When considering the number of references from different Member States, it will become immediately apparent that there are considerable variations. This article examines to what extent these variations may be explained by three structural factors, namely (1) population size, (2) willingness to litigate, and (3) Member State compliance with EU law. It is concluded that some - but not all - of the variations in number of references from Member State judiciaries may be attributed to structural factors rather than being merely a reflection of different Member State courts’ willingness to make use of Article 267 TFEU on such references (the so-called behavioural factors).