Environmental migration governance, like global migration governance more broadly, suffers from significant fragmentation both vertically - with actors at the international, regional and local levels - and horizontally - with the phenomenon addressed in part or, more rarely, as a whole under the auspices of a range of other ‘policy categories’ and associated institutions. Interests in environmentally-driven population movement can be identified across the fields of migration, environment, development, human rights, disaster management and humanitarian relief. Yet despite (or because of) the plethora of existing as well as potential governance mechanisms, processes and institutions, there is presently no coherent multilateral governance framework for environmental migration. The fact that the same is true of global migration generally provides the context for the present chapter’s examination of environmental migration governance. The particular features and challenges that it raises must ultimately inform the broader question of whether, and how, a unified global governance system for migration could and should be developed, and whether, and how, the regulation of environmental migration might fit into such a vision. Environmental migration is not a new phenomenon. Natural and human-induced environmental disasters have displaced people in the past and continue to do so. Nevertheless, the environmental events and processes accompanying global climate change threaten to dramatically increase human movement both within and across State borders. As far as actual numbers are concerned, there is no doubt that ‘current predictions are fraught with numerous methodological problems and caveats’. Yet most estimates suggest that between 200 and 250 million people will be displaced by environmental causes before 2050. The environmental impacts of climate change have been signalled as the key driver of this anticipated surge in migration. Evidently migration on this unprecedented scale demands a multilateral institutional response. Yet, environmental migration governance represents a significant challenge, not least because the content and parameters of the concept continue to be debated. There is at present no internationally agreed definition of what it means to be an environmental ‘migrant’, ‘refugee’ or ‘displaced person’, and, consequently, no agreed label for those affected. Questions of definition have clear governance implications, informing the appropriate location of environmental migration both procedurally - as an international, regional or local, developed and/or developing country concern/responsibility - and thematically - for example, within the existing refugee protection framework or under the UN Framework Convention on Climate Change. The viability and value of institutionalizing international cooperation and collaboration on international migration matters generally, and environmental migration particularly, depends upon how that phenomenon can and should be formulated as a discrete concept in law and policy. Such normative conclusions must be grounded in a thorough examination and assessment of the existing institutions and political processes that impact upon environmental migration and States’ responses to them.