Necessary deepening? How political groups in the European Parliament adapt to enlargement

Drawing on the theoretical literature on institutional change, group size and party organizations, this contribution explains the impact the 'mega-enlargement' of the European Union (EU) has had upon political groups in the European Parliament (EP). Presenting an in-depth analysis of their organizational adaptation, this work demonstrates that the widening of the EU is an important catalyst for organizational reform, and facilitates deepening. Additionally, describing the organizational reforms implemented to tackle enlargement, it also shows that party cohesion is the product of intense co-ordination activity within the groups, which starts at the committee level, rather than the use of disciplinary tools by the party leadership.