This document is an excerpt from the EUR-Lex website
The principle of subsidiarity is defined in Article 5 of the Treaty on European Union. It aims to ensure that decisions are taken as closely as possible to the citizen and that constant checks are made to verify that action at EU level is justified in light of the possibilities available at national, regional or local level.
Specifically, it is the principle whereby the EU does not take action (except in the areas that fall within its exclusive competence), unless it is more effective than action taken at national, regional or local level. It is closely bound up with the principle of proportionality, which requires that any action by the EU should not go beyond what is necessary to achieve the objectives of the Treaties.
There are two Protocols annexed to the Treaty of Lisbon that are key:
In the case of a breach of the principle of subsidiarity, the Committee of the Regions or EU countries may refer an adopted act directly to the Court of Justice of the EU.