The subsidiarity principle aims to ensure that decisions are taken as closely as possible to the citizen. Except in cases where the EU has exclusive competence, action at European level should not be taken unless it is more effective than action taken at national, regional or local level. Susbsidiarity is closely bound up with the principles of proportionality and necessity, meaning that any action by the Union should not go beyond what is necessary to achieve the objectives of the Treaty.
Subsidiarity was first introduced in the Treaty on European Union (Art. 5) in 1992. The Treaty of Amsterdam (1997) extended the principle, for example so that all legislative proposals are assessed for their impact on subsidiarity.
The Treaty of Lisbon further strengthens the principle. Specific changes include: greater consultation with the local and regional level when drafting legislative proposals; closer communication with national parliaments during the legislative process.