What motivates national judges to be either active in the preliminary reference procedure by expressing opinions in the requests they send to the Court of Justice or passive by not voicing their views? This Article sheds light on how national judges perceive the possibility of framing the cases they refer to the Court, for instance, by expressing an opinion in defence of the challenged national law. Based on interviews with Swedish judges, this Article shows that the respondents express opinions to provide the Court with information and to influence the development of EU law. The Article also uncovers what motivates national judges not to express opinions. These three previously untheorised motivations are: 1) protecting one’s reputation, 2) respecting the division of competences between the Court and national courts and 3) upholding the impartiality of the courts. Furthermore, the findings indicate that high court judges in particular are opposed to the inclusion of opinions in a request. In contrast, most of the interviewed lower court judges view the inclusion of opinions in the requests as practically mandatory. This Article proposes that this difference in attitudes towards opinions between high and low court judges originate from variations in professional norms regarding what constitutes appropriate behaviour.