Transnational environmental crime has become one of the largest criminal activities in the world. This chapter introduces the topic of transnational environmental crime by defining it, indicating the magnitude, scope, and harms, and identifying the various types of transnational environmental crime. In addition, the criminogenic asymmetries that attract transnational environmental crime are examined as well as the involved actors and joint crime ventures, the legal-illegal interfaces, and the role of scarcity, crime convergence, and conflict. The chapter will conclude with a reflection on the development of effective responses to transnational environmental crime, highlighting the importance to improve intelligence and cooperation, protecting the Global South from the Global North by harmonizing national environmental laws with due regard for local community needs and by adopting ecocentric approaches to prevent and react to transnational environmental crime.