The attack of 9/11 sparked off some crucial national security questions. One of such question is on how to proficiently counter terrorism without the flagrant violation of human rights by nation states. Unquestionably, issues on 'terrorism' and 'counterterrorism' are national security issues. Hence, this book investigates the inclination of the European Court of Human Right towards the issues of national security and human rights in the fight against terrorism. This is effected by evaluating the laws of the ECHR. Resultantly, this book sets out to critically review and ultimately revise existing legal/judicial conceptions of "national security". Therefore, the all-embracing intention of this book is to execute an exhaustive search for the formulation of a comprehensive definition of national security against the background of counterterrorism. To further illustrate the practicality of such a definition in the "fight against terrorism", the theory of 'preservative legitimacy' was propounded in this book. Through the ECHR case law, this book exposes the impunity with which sovereign states infringe on the principles of the rule of law while countering terrorism. Furthermore, this book questions the issue of the absolute nature of Article 3 of the ECHR with reference to deportation in the fight against terrorism. It exposes the challenges sovereign states face when deporting persons whom they consider threats to others and to the nation. This book contends with the trade-off of rights of a single individual (article 3 ECHR right of a terrorist/terrorist suspect whose activities has the potential to threaten national security) as opposed to the right to life of many innocent civilians. This book makes a case for the adoption of a comprehensive definition of national security, which could serve as a model for policy makers to adopt in the formulation and implementation of counterterrorism measures.