The Constitutional Convention process has sparked debates in many important areas of the EU politics. This study is a contribution to those debates and it touches particularly on four areas of future reform. This study wants to contribute, first, very generally, to the revitalized debate on deliberative politics within the EU and the fundamental question about the legitimacy of European decision-making. Second, more specifically, this study seeks to explore questions of the effectiveness of European decision-making and the buy-in and compliance of various stakeholders with the policy choices in an enlarged Union that gets ever complicated. Third, this study analyzes the innovative method of the Convention and the experiences made with it during the drafting of the Constitution with the goal of giving practical recommendations for the usefulness of the Convention method in general and for the design of successful future treaty negotiations. Forth, finally, and most specifically, this study traces causal mechanisms of arguing and bargaining in multilateral negotiations and, more broadly, seeks to inject a negotiation focus into EU research.