In recent decades, with the proliferation of domestic and international terrorism and other security threats, national security has got a global prominence as a buzzword to justify almost anything that States do to safeguard their security. National security is invoked to defend numerous counter-terrorism and other security measures ranging from the ubiquitous “global war on terror” to tightened immigration rules, various forms of detentions and extensive surveillance in and outside national borders. Individuals who are suspected of terrorism and security crimes have been subjected to, inter alia, indefinite security detentions, extra-judicial renditions, arbitrary expulsions and inhuman and degrading treatments and torture, all under the banner of protecting 'national security'. The amorphous nature of the term ('national security`) has given governments a 'carte blanche' to commit the most egregious human rights violations with the least political accountability and legal control. What does national security mean? To what extent may it be invoked to legitimately abridge fundamental human rights and freedoms? Whether or not national security is a justiciable matter before domestic and international judicial institutions? etc. are questions that international law offers no precise answers. This research examines these and other related issues by exploring the rules of international law regulating individual rights and freedoms through a comparative analysis of the jurisprudence of domestic, regional and international judicial institutions. On the basis of this analysis, the study argues that despite its ambiguity and the absence of any clear definition ascribed to it in international law, neither the meaning nor the application of national security is without a limit. A thorough review of the existing rules of international law and the practice of domestic and international judicial institutions clearly suggests that national security has definitional, contextual, temporal, procedural and other substantive limits in international law. These limits not only restrict the prerogatives of States to invoke the term but also give national security an international dimension in international law.