Pope Francis’s ecology encyclical, Laudato Si’, is an occasion to reconsider the Catholic Church’s myriad forms of engagement with modern science over the past four centuries. Four broad categories can chronologically and conceptually represent key phases in the Roman Catholic Church’s developing relationship to modern science. The first three are: how the Church coped with the rise of astronomy and physics in the 16th to 18th centuries; the era of geology and evolutionary theory in the 19th through early 20th centuries; and the era of global, life-altering technologies in the mid- to late 20th century. The scientific advances in each of these periods generated legacies for our current era of ecology and sustainability. It is this fourth phase that is represented by the new papal encyclical.