Drawing on an extensive data set and a large number of interviews with senior officials, diplomats and other practitioners, this report investigates the 32 months leading up to and following the enlargement of the EU in May 2004, i.e. from September 2001 through December 2006. The material collected for the analysis covers each piece of legislation adopted in the Council over a period of more than 5 years. The aim is to provide a body of quantitative data that illustrate some of the key changes that have occurred, and to describe and analyse these findings while also taking into account insights gleaned from interviews with the EU practitioners. Although some consequences of the enlargement may only become apparent once more time has passed, the data covering the elapsed time already allow for an in-depth analysis of many important aspects of Council decision-making. At the same time, they can provide useful indications of future developments.