15 Venerable Brethren and Beloved Children, as all everywhere and especially Catholic workers who are pouring from all sides into this Holy City, are celebrating with such enthusiasm the solemn commemoration of the fortieth anniversary of the Encyclical On the Condition of Workers , We deem it fitting on this occasion to recall the great benefits this Encyclical has brought to the Catholic Church and to all human society; to defend the illustrious Master's doctrine on the social and economic question against certain doubts and to develop it more fully as to some points; and lastly, summoning to court the contemporary economic regime and passing judgment on Socialism, to lay bare the root of the existing social confusion and at the same time point the only way to sound restoration: namely, the Christian reform of morals. All these matters which we undertake to treat will fall under three main headings, and this entire Encyclical will be devoted to their development.
Source: Quadragesimo Anno (Vatican.va)