This innovative book examines why national courts refer preliminary references to the European Court of Justice (ECJ), and what the referring court does with the answers. Jasper Krommendijk highlights the three core stages in the interaction between national courts and the ECJ: question, answer and follow-up, shedding new light on this under-explored area. Closing the gap between empirical interview data, and case law analysis, chapters use a unique combination of the two research methods to consider two current, and one former, EU Member States. The book demonstrates that judges extensively use the procedure and follow its outcome almost without exception, despite dissatisfaction and criticism regarding the absence of a true dialogue. By embedding the examples in the book in appropriate theory, this study will provide a useful read for students of EU law, particularly those wanting to better understand its consequences in the national legal order. Its recommendations for good practices in the ECJ and national courts will also be helpful to legal practitioners, judges and legal secretaries.