This book considers some of the most notable aspects of the legal response to the "war on terror" post- 9/11 and the use of technology to support them. It examines the shift from a criminal justice response to the creation of a parallel preventive system running in tandem with it. This system has tended to veer away from the commission of criminal offences or adherence to ordinary criminal justice safeguards. Such a preventive strategy relies on targeting terrorist suspects – those who it is thought may in future commit terrorist acts – and curbing their actions with the aim of preventing terrorist activity before it occurs.The book further considers the role that surveillance plays in the counter-terrorist efforts of state or non-state actors. It also evaluates the counter-productive effects that many of these measures have had.This book was originally published as a special issue of International Review of Law Computers & Technology.