Treaty of Nice

The Treaty of Nice was signed on 26 February 2001 by the then-15 member states of the European Union and entered into force on 1 February 2003, after a contested ratification process in Ireland. It amended the Treaty on European Union (Maastricht) and the Treaty establishing the European Community (Rome), with the primary goal of making EU institutions workable once membership expanded to include central and eastern European states.

Key reforms included:

• Reweighting of Council votes under qualified majority voting (QMV), increasing the relative weight of larger member states and introducing a "triple majority" requirement (votes, member states, and a verification of population share).
• Capping the European Commission at one Commissioner per member state, with provision to reduce numbers below the total once the EU exceeded 27 members.
• Extending QMV to roughly 30 additional policy areas previously requiring unanimity.
• Reallocation of European Parliament seats in anticipation of enlargement, setting a ceiling of 732 MEPs.
• Enhanced cooperation provisions, lowering the threshold for subgroups of member states to integrate more deeply without all others.

Ratification was disrupted when Irish voters rejected the treaty in a referendum on 7 June 2001. A second referendum on 19 October 2002, held after the Seville European Council issued declarations on Irish military neutrality, approved it.

Nice was widely regarded as a minimal, transitional fix. The unresolved questions it left — particularly around democratic legitimacy, the rotating presidency, and the EU's legal personality — drove the subsequent Convention on the Future of Europe and the failed Constitutional Treaty (2004), eventually replaced by the Treaty of Lisbon (signed 2007, in force 2009), which superseded most of Nice's institutional architecture. The Nice voting weights, however, continued to apply during a transitional period until the Lisbon double-majority system took full effect in 2014.