The field of security studies has traditionally been a core area of International Relations. In the recent decades it has also become one of the most dynamic and contested areas in the field, conducive to the emergence of versatile and transdisciplinary research agendas. This has unfolded in the context of a revival of strategic studies, first in the post 9/11 era, and now in the digital and post-pandemic world. The course surveys the field of contemporary international security theory and practice from the 1990s until today. It consists of three blocks: (1) revisiting the foundational concepts that have structured the discipline, including security dilemma, deterrence and security community; (2) examining the conceptual and sociological underpinnings of innovation in critical security studies, including through emancipation, securitisation, and insecurity approaches; (3) discussion of the most recent articulation of security problematique, including ontological and vernacular security, as well as science and technology studies and decolonial interventions.