Subsidiarity is the Catholic social justice principle which may be the least understood and taught and is one of the most important. Subsidiarity means that every issue should be handled by the lowest-level or least centrally-organized group whenever possible. The Catechism puts it this way:
Excessive intervention by the state can threaten personal freedom and initiative. The teaching of the Church has elaborated the principle of subsidiarity, according to which 'a community of a higher order should not interfere in the internal life of a community of a lower order, depriving the latter of its functions, but rather should support it in case of need and help to coordinate its activity with the rest of society, always with a view to the common good.'Here is a great explanation:
"God...entrusts to every creature the functions it is capable of performing, according to the capacities of its own nature. This mode of government ought to be followed in social life.
"Subsidiarity is opposed to all forms of collectivism. It sets limits for state intervention" (nn. 1883-1885).