Terrorism: Arriving at an Understanding of a Term.- The Due Diligence Principle Under International Law.- The Due Diligence Obligation of States in the Context of Non-State Actors That Engage in Terrorism.- Assessing the Due Diligence Obligation of States in the Context of Non-State Actors That Engage in Terrorism: Theoretical Issues.- Should National Security Trump Human Rights in the Fight Against Terrorism?.- Conclusion.