This chapter provides a foundation for the case made for ecological security by exploring the contours and limitations of existing discourses of climate security. After first examining the evolution of debates linking environmental change – and more directly climate change – to security, the chapter goes on to outline the contours and limitations of three key discourses of climate security: national security, international security and human security. These discourses emphasize the preservation of the nation state from external threat (national security), the preservation of the norms and rules of an international society (international security) and the protection of vulnerable human communities (human security). In the case of outlining the contours of each discourse, the chapter notes how the referent object is defined, who constitutes an agent of security, what means are envisaged to advance or protect security and the nature of the threat posed by climate change itself. In noting their respective limitations, the book provides a foundation for the elaboration and defence of ecological security.