This chapter discusses how the notion of ‘environmental security’ reflects both our fundamental concerns security and the changing context of security in the post-Cold War world. It examines the changing context of security in which environmental factors have a major role to play. The post-Cold War period is defined by changed priorities, and it has become commonplace to reconsider the concept of security in this context. It is, however, rather less common to consider the environmental dimensions of security. Thus environmental change presents security concerns which are qualitatively different from traditional security threats, and may even represent the basis for a broad shift in social values. Furthermore, global issues such as environmental change dislocate conventional points of reference in state security and national interest. The idea of environmental security necessarily reflects a ‘critical’ approach to the concept of security because of the diffuse characteristics of the source of insecurity which environmental change implies.