During the last few decades important shifts have taken place in the realm of criminal law, broadening its relevance on an international level. A variety of criminal conduct increasingly features an extraterritorial element. Penal actions are thus in many instances no longer confined to one State’s territory, but rather involve a variety of jurisdictions and trigger the transnational enforcement of criminal law. These developments have led to an enhanced interaction between various criminal justice systems and consequently require a raised awareness and understanding of different national rules allowing for cross-border prosecution by national agencies and of the international frameworks for cooperation in criminal matters. Furthermore, and even more important, the shift in approach calls for new solutions regarding the conflicts of interests between those seeking to prevent and repress crime, the individuals alleged to have committed the offenses and the victims of crime. Up to now, public authorities as well as lawmakers have generally reacted on a case-by-case basis. This approach, however, does not allow for more general considerations relating to the good administration of justice and legal certainty. It seems thus necessary to establish guidelines, which solve these conflicts of interests and which strike a balance between public concerns and legitimate individual interests. The project’s goal is to establish general principles for transnational criminal law, which can be engaged to guide decision makers in the process of resolving conflicts of interests arising in instances of cross-border law enforcement. These principles should encompass, inter alia, the principle of legality, the principle of guilt as a prerequisite of criminal liability, fair trial rights and procedural safeguards, an internationalized ne bis in idem principle, judicial control and the right to an effective remedy. They can be deduced from the different fields of transnational criminal law, namely the rules on the applicability of domestic criminal law, the law of mutual legal assistance in criminal matters, European Criminal Law and International Criminal Law stricto sensu, and must also include safeguards based on fundamental and human rights.