Post-9/11 the equilibrium between security and liberty has been subject to intense political and philosophical interrogation. The metaphor of balance, although perilous, is so pervasive as to demand scrutiny of what lies in the scales, what tips them, and in whose interest. Though international and constitutional lawyers have dominated the debate about balance, the experience of criminal justice suggests that articulating a principled approach provides greater prospects of protecting rights against unwarranted erosion. This more modest approach imposes structural and procedural safeguards through the twin engines of judicial oversight and unremitting defence of due process. In this way it may be possible to enhance collective security against terrorism without diminishing individual security against the state.