This month we celebrate the 130th anniversary of Rerum Novarum, which has come to be regarded as the origin of modern Catholic Social Teaching. But it also marks the 60th anniversary of Pope John XXIII's first social encyclical, Mater et Magistra, which was itself a revolutionary document in its own way and time. Indeed, only four years later, it would become the most cited document in the Vatican II Pastoral Constitution on the Church in the World of Today,