Catechism of the Catholic Church
1883 - Socialization also presents dangers. 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 co- ordinate its activity with the activities of the rest of society, always with a view to the common good."7
1885 - The principle of subsidiarity is opposed to all forms of collectivism. It sets limits for state intervention. It aims at harmonizing the relationships between individuals and societies. It tends toward the establishment of true international order.
7 - CA 48 § 4; cf. Pius XI, Quadragesimo anno I,184-186
Explanation about subsidiarity starts at 4:17 (4 minutes 17 seconds)