The Constitutional Treaty, which attempted to establish a constitution for Europe, never went into force because of “no” votes in referendums in France and the Netherlands. It did not involve far-reaching changes in what the European Union does, nor did it revolutionize how the institutions work. The pillar structure of the existing treaties was replaced with a single Union, but without fundamentally changing how foreign, security and defense policies were decided. A “foreign minister” was created that merged the roles of High Representative in the Council and Commissioner for External Affairs, and the European Council was established as a separate, treaty-based institution. A simple double majority qualified majority voting (QMV) procedure was introduced in the Council, and the use of QMV was extended to many more policy areas.

Given these modest reforms, what was particularly remarkable about the Constitutional Treaty was how it was negotiated. In contrast to previous major treaty reforms, the Constitutional Treaty was prepared by a more inclusive, parliament-like convention that was composed of representatives from national parliaments, the European Parliament, the European Commission, and member state governments. Although the European Convention was followed by a more traditional intergovernmental conference (IGC), the draft produced by the Convention surprisingly formed the status quo during the IGC. Therefore, the use of the Convention method to prepare treaty reforms sparked considerable interest among scholars who have explored how the change impacted who won and lost in the negotiations, and what types of bargaining strategies were most effective.