The melting of glaciers and the increasing frequency of extreme weather events, droughts, and flooding are powerful reminders of climate change and signals that we have entered the Anthropocene (Crutzen 2002) -a new geological epoch in which the future of the planet depends on human actions, and which has 'no analogy' in the Earth's history (Dalby 2009, p. 11). Human action has become so powerful and pervasive that it is comparable to a geological force that transforms the planet in unprecedented ways. Nature, the environment and climate are no longer stable backgrounds against which human history and actions unfold. This requires humans to embrace the challenges of this new condition, its complexity and uncertainty. Climate change is emblematic of this shift, as it anticipates many challenges of the Anthropocene. New potentially catastrophic threats -the possibilities of abrupt climate change or the massive extinctions of species -emerge, while concerns about access to water, food and energy remain relevant and are aggravated by climate change. Conflict and social instability may follow or be exacerbated. Not surprisingly, some of these challenges have been addressed as security issues, both because of the concerns that these problems raise for states and peoples, and the power of evoking security to mobilize and legitimize action (Trombetta 2021).Attempts to link climate change and security date back to the 1970s, when apprehensions about anthropogenic changes in weather patterns started to develop. Since then, climate change has been included in national security strategies and has been brought to the discussion of the United Nations Security Council (UNSC) on more than one occasion (Scott 2015 and Chapter 13 in this volume). There is extensive academic and political debate on the subject. 1 Yet, the term 'climate security', which is used in the literature, remains ambiguous and contested, as does the very consideration of climate change as a security issue.Establishing a link between climate change and security is not a straightforward process. Far from being self-evident, it implies a set of political choices on the kinds of threats that need to be considered, whose security is at stake, and the means to be employed. Once questioned, these choices reveal deeply seated assumptions on what counts as security and the ways of providing it and prompt reflection. For many, security is still associated with the survival of the state, its core values and the legitimation of exceptional measures. The link also requires conceptual and theoretical reworking of the way security is understood and provided, as many of the threats posed by climate change do not fit the traditional security agenda and logic. They question, for instance, the protection of a territory against external threats, using defensive, reactive measures and, that, in turn, challenges many of the political categories on which we moderns operate and think through.This Handbook explores the emergence of climate change as an international security issue,...