The topic of this thesis is the use that member-state governments make of their opportunity to submit legal arguments in preliminary reference proceedings at the Court of Justice. Which Member States submit observations and which do not? What motives do Member States have for their submissions, and what influence do they have on the development of EU law? Can their influence be accommodated within existing models of European legal integration? And can we learn more about the Member States' policy preferences from their submissions to the Court?

The study of EU legal integration stands on the boundary of political science and law, and researchers have tended to develop theories using their own disciplines' perceptions. In doing so, political scientists have neglected judicial reasoning, while lawyers have overlooked the political and economic contexts of cases and the non-legal actors involved in them. This thesis uses both quantitative and qualitative empirical methods to develop a conceptual framework for evaluating different theories of EU legal integration.

The provisions that enable member-state governments to present arguments to the Court are introduced, and the data sources evaluated. The variations between the Member States are discussed, before states' motives are examined in more detail, and a taxonomy developed. The elements of the taxonomy are then demonstrated via the submissions of three chosen states: Denmark, Ireland and the UK. It is argued that governments' observations to the Court form part of a wider discourse between the Member States and the EU, in which they may better represent a Member State's true preferences than its voting behaviour at the Council. The thesis concludes that theoretical models of the relationship between governments and the Court must account for the variation between the Member States, their motives, and the Court's use of their submissions.