The preferential option for the poor (POP) has become an essential element of Catholic social teaching (CST). There are two major currents of interpretation of this preferential love of the poor. One interpretation is that of Latin American theology of liberation, where the expression originated. Another one is the position taken by the magisterium, especially by the papal magisterium, that Pope Francis has developed and modified, nevertheless remaining in the range of the precedential magisterial texts, as I try to show. In this chapter I concentrate on the way the Catholic magisterium has presented the preferential option for the poor. The Second Vatican Council and the various General Assemblies of the Latin-American Bishops’ Conference (CELAM) after their second gathering in Medellín in 1968 are of paramount importance to the development of the POP.