The North-South divide is one of the central political characteristics of the UN climate change negotiations. But while the Group of 77 coalition has been the main negotiating group for the South, developing countries have often faced challenges to their unity, magnified by the recent establishment of smaller negotiating groups. How has 'the South' hung together? This thesis investigates how developing countries have formed negotiating groups over the two decades of the UN climate negotiating process. It explains the origins of the different negotiating groups that have formed over this time, as well as the timing of their emergence and the scope of their membership. In particular, while scholarly attention has focused on the G77, Alliance of Small Island States (AOSIS) and most recently the Brazil-South Africa- India-China (BASIC) coalition, this thesis corrects the relative neglect in understanding the many other negotiating groups that have formed. While conventional explanations highlights the shared material interests that underpin group formation, this thesis advances a constructivist argument that emphasises instead the importance of collective identities in shaping norms of 'appropriate association' – the social bases of whose one's friends and allies are. It highlights the regional basis for many of these negotiating groups that cut across shared material circumstances, and draws upon historical institutionalist insights on critical junctures and path dependence to place this larger pattern of Southern coalition formation in the appropriate historical and institutional context of the UN system. It demonstrates the continuing persistence of countries identifying as the 'South', where despite changing material circumstances and disagreements among developing countries, the salience of the G77 as the constitutive institution of this identity remains. Above all, in investigating the processes of coalition formation among developing countries in the climate context, this thesis deepens scholarly understanding about the contemporary meaning of the 'South'.