The creation of an economically integrated Europe, based on free circulation across open borders, has probably facilitated an increase in transnational crime. One response to this phenomenon has been to try to create an integrated European criminal law. But legal integration will not magically solve all the problems related to transnational crime. Indeed, it may create problems of its own. By favouring efficiency (that is, repression) over legitimacy (the protection of fundamental rights), it favours a criminal justice policy oriented towards ‘security’. By imposing the same rules throughout Europe, it disturbs the internal consistency of national legal systems. Nevertheless, the phenomenon of legal integration, facilitated by new legal instruments such as framework decisions, continues to develop. We might therefore ask ourselves, as an introduction, why this is so.