Résumé : The European Union has developed since the mid-1990's its own policy to prevent and fight against trafficking in human beings (THB). This phenomenon constitutes a threat to the internal security of the European Union, and it also entails severe violations of fundamental rights of its victims. While taking into account the evolution of the definition of THB, as well as the development of a EU multidisciplinary, integrated and holistic approach to THB, my doctoral research focuses on the external dimension of this policy. It is divided in three main parts. Firstly the analysis of the EU acquis in this field allows to determine the external competences at its disposal to promote the transposition of its standards beyond its borders. Special attention is given to the EU's externalisation efforts towards the candidate and potential candidate countries of the Western Balkans. The second part focuses on the interactions between the European Union and the other actors active in this field, being intergovernmental organisations, civil society organisations, or States. The objective is here to demonstrate that their interactions lead to the emergence of harmonized objectives and measures to combat THB in a comprehensive way. Finally the third part aims at assessing the implementation of European and international standards in national legal orders. Two case studies have been selected here: Belgium and Bosnia and Herzegovina, and their national legislations and policies are examined in order to assess whether they comply with these standards and implement a comprehensive approach to fight against THB.