Environmental security was once considered a national security issue in the US, but it later disappeared from the government's agenda. This book examines this shift in policy to develop a new theory that helps understand the intentions of key players and allows moral evaluations in the environmental security field. By interviewing former US environmental security officials, the author sheds light on the relationship between environmental security and securitisation theory. The findings of this study will interest those in international relations, security studies, and environmental politics.