The norm of climate security as analysed in this chapter calls for climate change to be conceived of as a threat to international security, with consequent implications for governance of the issue. The majority of states have now accepted in their national policymaking that climate change poses a security threat (The Amer ican Security Project 2016). At a global level, the United Nations Security Council held a debate on climate and energy in 2007 and a second debate in 2011, after which it issued a presidential statement expressing concern ‘that possible adverse effects of climate change may, in the long run, aggravate certain existing threats to international peace and security’ (United Nations Security Council 2011). A further informal ‘Arria-formula’ meeting was held in 2013, and in 2015 the issue of climate risks was again discussed in an Arria-formula meeting on state fragility and in a debate on security matters of concern to small island developing nations (Center for Climate Security 2015). As yet, however, there has been no Council resolution on the subject. According to von Lucke, Wellmann and Diez, the fact that climate change is a security concern is now ‘firmly established on the political agenda, even though the implementation of concrete policies is disputed’ (von Lucke, Wellmann and Diez 2014, 857). Although it is not necessarily logically incompatible with other framings of the climate change issue, the norm of climate security situates climate change policy squarely within the arena of high politics. Analysis of the reception of norms that frame issues in terms of security threats can be enhanced through drawing not only on the literature on norm dynamics but on that by theorists of securitisation. This chapter begins by situating the current analysis within both bodies of literature. It proceeds to identify the norm entrepreneurs and antipreneurs, the key sites of resistance, and the discursive and other forms of resistance to the norm. Application of the antipreneur concept has facilitated drawing a clear distinction between the roles played by the various actors, focusing attention on the discursive practices that have been used to oppose the norm and highlighting the need to situate analysis of the promotion and reception of the climate security norm within a complex normative interplay, as opposed to interpreting the climate security trajectory as one discreet normative development in climate change politics.