Carole Billet studies different issues:

- The differentiated participation of Member States in the European Union's action on the international scene

Analysis of the development of differentiation in European Union law (and in particular the evolution of concessions granted to the United Kingdom) and its impact on the image of the European Union as an international player. Study of the use of opt-outs in the context of external agreements (e.g. for the accession of the European Union to international conventions) or unilateral instruments affecting the external action of the European Union (such as financial instruments), including study of the arrangements for coordinating action between the European Union, its third party partners with whom it cooperates, and Member States not participating in the instrument. Study of the impact of enhanced cooperation between some Member States on the development of the European Union's external action.

- Decentralised agencies of the European Union

The question of the role of EU agencies in the institutional landscape of the European Union is nothing new and now seems more relevant than ever, because of the growing increase in their competences. EU agencies are more and more important and recognised players on the international scene, which regularly raises problems of consistency with the action taken by the Union's institutions. An in-depth analysis of the place and role of agencies in the Union's action will be carried out, in particular to analyse the characteristics of the Union as a global player (Frontex in the context of the migration crisis, Europol in the context of cooperation with the United States on terrorism).

- EU action in the field of migration and asylum

Analysis of the European Union's external action in this field and study of the evolution of the legal instruments used for cooperation with its partners. Global analyses to take into account the different levels of action (national, European and international) in order to measure the relevance and coherence of the European Union's action.

- Cultural law in the European Union

Study of the links between culture and other policies and actions of the European Union, the external dimension of cooperation in the field of culture, and fundamental cultural rights.