"In a European Union increasingly worried about the security of its citizens and its territory, how should the European Parliament make policy decisions on these issues? In the past, its open defence of civil liberties and human rights have sparked recurring conflicts with member states on the European Council. Since 2005, the European Parliament has gained the power to co-decide in most internal security matters and can also give consent to international agreements. Its full participation in decision-making led to the expectation that the emphasis on security would decrease yet these last few years have seen continuity rather than change in this policy area. This study investigates why the formal empowerment of the European Parliament did not lead to a new balance between security and liberty. It argues that, in its new position as a full decision-maker, the European Parliament faced a crucial trade-off: in order to be accepted as a legitimate and effective partner in inter-institutional negotiations, it had to abandon its traditional positions and accept that security would remain the cornerstone of this policy area. "-Provided by publisher.