How has the European Union been affected by the recent enlargements that brought its membership to a diverse group of twenty-seven countries? This paper answers this question by examining whether enlargement has changed the way in which controversies are resolved. In particular it formulates and tests several competing models of legislative decision-making and identifies the relative accuracy of the predictions of decision outcomes made by each model. Among the models formulated and tested is a procedural model, according to which the rules of procedure structure the decision-making process. As alternatives to the procedural model, several bargaining models, including two theoretically and empirically distinct variants of the Nash Bargaining Solution, are formulated and tested. These bargaining models make fundamentally different propositions about the informal bargaining process through which actors’ policy demands are transformed into outcomes. The analyses are performed on a new dataset with information on the policy positions of each of the member states in the Council, as well as the Commission and European Parliament, on 331 controversial issues raised by 125 of the most important legislative proposals from the period 1999-2009. In addition to testing the accuracy of the models’ predictions before and after enlargement, this study also examines the likely impact of the new double-majority voting system in the Council that will be brought in by the Lisbon Treaty.
