Quadragesimo anno (kwa.draˈd͡ʒɛː.si.mo ˈan.no) (Latin for "In the 40th Year") is an encyclical issued by Pope Pius XI on 15 May 1931, 40 years after Leo XIII's encyclical Rerum novarum, further developing Catholic social teaching. Unlike Leo XIII, who addressed the condition of workers, Pius XI discusses the ethical implications of the social and economic order. He describes the major dangers for human freedom and dignity arising from unrestrained capitalism, socialism, and communism as practised in Russia. He also calls for the reconstruction of the social order based on the principles of solidarity and subsidiarity.
Essential contributors to the formulation of the encyclical were the German Jesuits, Roman Catholic theologians and social philosophers Gustav Gundlach and the Königswinter Circle through one of its main authors Oswald von Nell-Breuning.
Pope Pius XI issued his encyclical exactly forty years after Rerum novarum. In the interim there were other papal statements from Leo XIII, and also the encyclical Singulari quadam of Pius X. Pius XI subtitled his encyclical Reconstruction of the Social Order. In the first part he reviews and applauds the encyclical of his predecessor. The Catholic Church can be credited with participating in the progress made and contributing to it. It developed a new social conscience.
The Church has a vital role in discussing social and economic issues, not in their technical, but their moral and ethical aspects. This includes the nature of private property, concerning which several conflicting views had developed within the Catholic Church. Pius XI proclaims private property to be essential for the development and freedom of the individual, which are Christian values not to be denied. But, says Pius, private property has a social function as well, and it loses its moral value if it is not subordinated to the common good. Therefore, governments have a right to pursue redistribution policies, and in extreme cases to expropriate private property.