Quadragesimo Anno is an encyclical issued by Pope Pius XI in 1931, marking the 40th anniversary of Rerum Novarum, the first modern social encyclical. It addresses the social and economic issues arising from the aftermath of the Great Depression and critiques both unregulated capitalism and socialism. The document emphasizes the importance of social justice and the role of the state in promoting the common good. The encyclical advocates for the principle of subsidiarity, which suggests that decisions should be made at the most local level possible. It calls for a more equitable distribution of wealth and the need for cooperation between different social classes to achieve a just society.