The research community of ontological security scholars is vibrant and wide-ranging, defined by a conceptual core and by the themes through which scholars register their disagreements. In this special issue we have collected some of the work that has been produced or inspired by discussions and meetings during the last few years. The goal is to showcase some of the breadth of insights and possibilities on the topic of ontological securities and insecurities in world politics. Thus far, International Relations scholarship on ontological securities in world politics has been varied, focusing on different referent objects (individual, society, group, state), different political outcomes (cooperation, conflict, violence; stability or change) and different methods (quantitative, qualitative, discursive). While on the face of it such differences would seem to pose a challenge to the goal of developing a coherent research agenda, we have found the range of work and diversity among ontological security scholars to be exceptionally productive, leading already to cross-fertilisation and the deepening of our own approaches, while also inspiring new collaborations. The articles in this special issue discuss the subjective and foundational dimensions of ontological security in philosophical, existential and empirical terms and approach the ‘level-of-analysis’ problem from new perspectives.