Enhanced cooperation allows those countries of the Union that wish to continue to work more closely together to do so, while respecting the legal framework of the Union. The Member States concerned can thus move forward at different speeds and/or towards different goals. However, enhanced cooperation does not allow extension of the powers as laid down by the Treaties, nor may it be applied to areas that fall within the exclusive competence of the Union. Moreover it may be undertaken only as a last resort, when it has been established within the Council that the objectives of such cooperation cannot be attained within a reasonable period by the Union as a whole.
The general arrangements for enhanced cooperation are laid down by the Treaty on European Union (Title IV). In principle, at least nine states must be involved in enhanced cooperation, but it remains open to any state that wishes to participate. It may not constitute discrimination between those participating and the other states. Any acts that are adopted within the framework of such cooperation are binding only on the participating Member States and do not constitute a part of the acquis. Enhanced cooperation must further the objectives, protect the interests and reinforce the integration process of the Union.
In addition to the general regime, special arrangements are laid down in the Treaty on the Functioning of the European Union (Title III). Following the approval of the European Parliament on the Commission proposal, the Council grants Member States’ requests to initiate enhanced cooperation. Decisions authorising cooperation in the field of the common foreign and security policy (CFSP) are taken unanimously by the Council, following the opinions of the High Representative of the Union for Foreign Affairs and Security Policy and the Commission. Voting takes place only among those members of the Council that represent the Member States participating in enhanced cooperation. Notifications on participating in enhanced cooperation already in progress are given to the Council and the Commission and, in matters relating to the CFSP, to the High Representative. Apart from decisions concerning military and defence matters, the Council may, under certain circumstances, decide unanimously to act by qualified majority or under the ordinary legislative procedure.
The Treaty of Amsterdam incorporated the "enhanced cooperation" concept into the Treaty on European Union as regards judicial cooperation on criminal matters and into the Treaty establishing the European Community. The Treaty of Nice introduced major changes aimed at simplifying the mechanism. In particular, a Member State may not oppose the establishment of enhanced cooperation as originally allowed by the Treaty of Amsterdam. To further improve cooperation and to make it more purposeful, the Treaty of Lisbon introduced additional modifications mainly related to the procedure for the initiation of enhanced cooperation, as well as decision-making within the framework of such cooperation.