This study focuses on the interfaces between legal and illegal actors engaging in transnational crimes. These interfaces can be quite complex as the cases of Udo Proksch and Cornelius M. illustrate. Due to this complexity, such cases and the related interfaces cannot be caught easily with clear-cut and mutually excluding categories like 'transnational (organized) crime' versus 'legitimate' businesses and government agencies. The boundaries between transnational crime, terrorism, corporate crime and state crime fade away as one focuses on such concrete cases. As the rest of this study will show, the characteristics of these cases appear to be far more representative of transnational crimes in general than usually assumed. For a number of reasons, a study that focuses solely on interfaces can be an important and necessary addition to the existing criminological studies. The first reason has to do with the mentioned lack of systematic studies of the interfaces between legal and illegal actors. The second reason has to do with the observation mentioned above. By studying interfaces between legal and illegal actors, the rather thin boundaries between transnational crime, corporate crime and other types of crime become clear. Only after these boundaries are crossed, or even leveled, transnational crimes can be understood from a broader perspective. From such a perspective, transnational crimes are always taking place against a specific background of economic factors, state policies and legislation, as well as other factors. Thirdly, a systematic study of interfaces can help to indicate the different types and causes of interfaces that can be found in different types of transnational crime. Finally, as the role of legal actors with all kinds of transnational crimes is clarified, more effective legislative and policy instruments can be designed to counter this role. The first half of this study will be based on the literature on transnational crimes. The second half will describe the empirical research of the illicit art and antiquities trade that was done specifically for this study. The illicit art and antiquities trade was chosen for several reasons. On the one hand because it is a type of crime that is known for its interfaces between legal and illegal actors and on the other hand because empirical studies of this type of crime have been scarce, especially from a criminological perspective.