Fr. Drew Christiansen, S.J., who served as an expert adviser to the Holy See delegation to the 2017 UN conference on nuclear disarmament, recounts the role of the Vatican in deliberations on the Treaty on the Prohibition of Nuclear Weapons. Christiansen notes five key points: (1) the humanitarian focus of the conference; (2) the place of the ban in the architecture of nuclear disarmament; (3) the role of the IAEA and other authorities under the treaty; (4) the place of appeals to ethics in the treaty; and (5) the (non)usage of the language of peace. He concludes by describing several ongoing challenges to disarmament efforts, including North Korea's nuclear regime, the lack of involvement of nuclear-possessing states, and the slow process of establishing new international norms regarding disarmament. The article was published in the Journal of Catholic Social Thought.