The Encyclical Letter Quadragesimo anno (QA) of Pope Pius XI is of great importance in the recent tradition of the magisterium of the Bishop of Rome around what is conventionally called teaching or social doctrine of the Church, triggered by the Encyclical Letter Rerum Novarum (RN) of the Pope Leo XIII in 1981. As the title indicates, the QA was written on the occasion of RN’s fortieth anniversary in 1931. It has a character of continuity and novelty in relation to this encyclical. It is not a mere repetition or even a mere explanation of the RN. It advances in terms of precision, development, application and even additions. In this sense, it plays a decisive role in the dynamic-procedural character of the Church s social teaching. But it is not a simple and easy to understand text. Hence the importance of this work, which, as its subtitle indicates, intends to be a guide for reading this encyclical. It begins by indicating the socio-ecclesial context in which it arises and to which it seeks to respond. It provides a panoramic presentation of its fundamental structure and content. And he concludes by highlighting some important points for its proper understanding and interpretation.