Subsidiarity is a principle guiding the sharing of competences for policy and law-making between the European, national and sub-national (regional and local authorities) levels.
Specifically, it is the principle whereby the Union does not take action (except in the areas which 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 Union should not go beyond what is necessary to achieve the objectives of the Treaty.