One year ago, Pope Francis published his landmark encyclical letter, Laudato Si’: On Care for Our Common Home. Rarely before has an encyclical been so widely anticipated or generated so much commentary beyond theological circles, or managed to accomplish so much in one document: a symphonic synthesis of theology, the natural and social sciences, philosophy, Catholic social teaching, and the poetry of prayer. In the realm of theology alone, the encyclical addresses, explicitly or implicitly, theologies of creation, incarnation, redemption, and eschatology, as well as ecclesiology and ethics, and presumes and advances church teaching on the interpretation ofScripture, the preferential option for the poor, and the conversion to which the gospel calls us. It calls upon the resources of political science, economics, and social and cultural anthropology to advance its arguments. And, of course, the encyclical directly addresses the fact of human-induced climate change and the ethical as well as theologicalimplications for our time of this momentous development. It played a significant role in the relative success of COP20, the recent Paris Climate Summit. For these and other reasons, one of the authors in this special issue describes Laudato Si’— without exaggeration in my opinion—as “the most important encyclical ever written in the history of the Catholic Church.”