Laudato Si’, Pope Francis’s historic encyclical on the environment, was issued in 2015. As the first encyclical devoted entirely to the environment and related social justice issues, it represented a watershed in the church’s engagement with such urgent challenges as climate change, environmental degradation, and the fate of the poor. This volume joins the full text of Laudato Si’ with reflections by Sean McDonagh, one of the foremost Catholic proponents of ecological awareness. Aside from reviewing the history of Catholic teaching and the environment, he elaborates on several of the specific themes in the encyclical—climate change, biodiversity, water scarcity, the threats to the ocean, and the crisis of food. He concludes with prescriptions about what must be done to turn the pope’s vision into a program of effective action. Each of us has a role to play. As Pope Francis observes, “All it takes is one good person to restore hope.”