Although the roots of subsidiarity predate Christianity, we can usefully explore encyclical teaching to appreciate how the Catholic Church has given intelligible expression to this concept in the midst of her broader social teaching. The paradox of subsidiarity is that it mandates contradictory things: requiring on the one hand that the state should not interfere with the internal life of civic associations and on the other hand that the state should provide assistance to those associations when such assistance is necessary. Rather than using the language of "positive" and "negative" subsidiarity (which, it is argued, is not especially helpful because it perpetuates the sovereigntist tendency to see the state as the locus of all authority), this chapter focuses on how the encyclicals illuminate (1) the nature of subsidiarity, as neither freestanding nor abstract; (2) subsidiarity’s political purposes (increased participation in decision making by actors who are more proximate to need and therefore better placed to reach good outcomes more efficiently), moral purposes (protection of associational freedom and avoidance of totalitarianism), and final purposes (protection of that charity which can never be mediated through bureaucracies); and (3) the operationalisation of subsidiarity, which can be promoted or inhibited through the action of law.