This introduction describes recent development in the climate-security debate and policymaking, in particular how the debate has advanced as actors have connected two deadly conflicts – the Darfur and Syria civil wars – with climate change. The chapter highlights how the securitization of climate change has accelerated, leading to the establishment of several new policies and institutions, in spite of the ongoing disputes about the evidence for climate-security links. It then identifies the main purpose of this book: to understand the contradictory coexistence of disputed evidence and accelerating securitization of the presumably science-driven issue of climate change. The chapter then highlights how climate-security is a part of a broader trend of nexus formation in international politics, and how knowledge resources are a central feature of efforts to link climate and security. Against that background, the chapter outlines the actor-network-theory-based approach of this book, and the structure of the chapters that follow.