This chapter introduces the book, Climate Security in the Anthropocene—Exploring the Approaches of United Nations Security Council Member-States. Climate change is increasingly positioned as a security issue. A number of influential governance actors including states, international organisations, and civil society groups now connect climate change to a variety of security threats such as armed conflict, disasters, low socio-economic development, and fragile governing institutions. These threat perceptions have translated into political action and have led to the formation of a complex constellation of governance actors in response. In particular, over the past fifteen years both permanent and non-permanent member-states of the United Nations Security Council (UNSC) have been instrumental in constructing and responding to climate security threats. This introductory chapter presents the overall aim of the book, which is to analyse whether the concept of security has shifted over time with respect to climate change, and if so, how these shifts have occurred in state practices. It begins by tracing the evolution of climate security in academic scholarship and in the UNSC. It then presents the theoretical framework of the book, which distinguishes between three ideal-types of climate security: national security, human security, and ecological security. It concludes by outlining the methodology of the book, which is comprised of fifteen case study chapters that explore the various ways in which member-states that sat on the UNSC between 2018 and in 2020 constructed and responded to climate security threats.