This thesis examines the relationship between security, politics and revolution. It analyzes securitization theory’s assumptions about politics and how these assumptions underpin processes of securitization. This analysis presents an argument that securitization theory assumes existence of what the thesis calls an established political realm in which processes of securitization take place. The central research question asks how security is constructed when an established political realm is not present and what are the implications for securitization theory. The thesis argues that revolutions offer one example of situations where the political conditions assumed by the theory are missing. The research question is therefore applied to six case studies drawn from the French and the Russian revolutions. The cases cover the declaration of war on Austria in April 1792, the June/July 1917 offensive, the civil wars accompanying the two revolutions, and the rise of new security institutions within both revolutions. The case studies are arranged in a comparative scheme. The thesis aims to contribute to a better understanding of securitization theory and, by extension, the concept of security and its relation to politics.