Abstract: The Academy’s Eighteenth Plenary Session was the second of its three projected meetings devoted to reflection on the themes of Pope John XXIII’s encyclical Pacem in Terris in the light of the changes that have taken place since that historic document was issued nearly fifty years ago. The Academy began its examination of the current status of those themes in 2011 with a Plenary devoted to the encyclical’s engagement with the modern human rights project, focusing specifically on religious freedom as emblematic both of the aspirations and the dilemmas of the universal human rights idea. This year, in an outstanding program coordinated by Professor Russell Hittinger, we turned directly to the global quest for peace. The Plenary yielded a sobering answer to the question that Pope Benedict had posed to representatives of the world’s religions who gathered at Assisi last year to pray for peace: “What is the state of play with regard to peace today?” Many speakers noted how much the global landscape had changed since Pacem in Terris addressed the threats to peace in 1963. Yet there was general consensus that today the reign of peace remains elusive, menaced by regional conflicts, civil wars, the proliferation of weapons of mass destruction, and the rise of terrorism by non-state actors, some claiming religious motives.