Security studies has been slow to accept critical challenges to its problematic, and these have often been met with hostility and deliberately marginalized. This article responds to some of the critiques, and outlines the main elements of a critical engagement with security studies. It discusses the intellectual and `disciplining' power of rationalist and neorealist security studies scholarship, and highlights some of the practices that marginalize critical scholarship. It then overviews the rich and diverse threads of current research within `critical security studies', and emphasizes the central themes of its research agenda: how threats and appropriate responses are constructed; how the `objects' of security are constructed; and what the possibilities are for the transformation of 'security dilemmas'. It summarizes the six central claims (concerning the constitution of the actors of world politics, its dynamic and constructed nature, the concomitant epistemological claims and methodological tools, and the purpose of theorizing) that are the hallmark of a critical approach to security studies. Finally, it clarifies what these claims do and do not entail for research and practice in international security studies.