Subsidiarity is an organizing principle stating that matters ought to be handled by the smallest, lowest, or least centralized competent authority. The Oxford English Dictionary defines subsidiarity as the idea that a central authority should have a subsidiary function, performing only those tasks which cannot be performed effectively at a more immediate or local level. The concept is applicable in the fields of government, political science, cybernetics, management, military (Mission Command) and, metaphorically, in the distribution of software module responsibilities in object-oriented programming. Subsidiarity is, ideally or in principle, one of the features of federalism, where it asserts the rights of the parts over the whole.
The word subsidiarity is derived from the Latin word subsidiarius and was first described formally in Catholic social teaching . The concept or principle is found in several constitutions around the world.
Subsidiarity is also a tenet of some forms of conservative or libertarian thought. For example, conservative author Reid Buckley writes: