This chapter assesses the role of multilateral diplomacy in strengthening nuclear security after the nuclear summit process ends in 2016. Nuclear security diplomacy is taken to mean communications, discussions, and negotiations among states, especially through high-level gatherings of government representatives, and other stakeholders, notably industry and civil society. Diplomacy may, at first glance, seem to be a laughingly fey response to the threat of nuclear terrorism. One of the challenges in ensuring comprehensive nuclear security is the array of institutions, mechanisms, and arrangements that deal with the issue, either at a broad policy level or in more substantive terms. The Council would also likely play a critical role in reacting to a major nuclear terrorism incident. However, both UNGA and the Council have comprehensive agendas that only allow episodic attention to nuclear security and cannot therefore be expected to play a regular, attentive diplomatic role in this field.