Within the scope of its attributed powers, the EU has a competence to enter into international

agreements with third countries and other international organisations. However, the individual EU

Member States have not, as a result, lost their capacity to enter into international agreements.

The Member States losing this competence remains the exception and in most cases there is a

possibility and sometimes even a necessity for both the EU and the Member States to be parties to

an international agreement with a third country or international organisation. EU jargon refers to

such a situation as one of ‘ixity’ the international agreement being a ‘ixed agreement’

The Treaty of Lisbon, in force since December 2009, has reformed the rules governing the EU’

external relations and thereby added a further layer of complexity to mixity: even if the EU Court

of Justice has allowed for mixity, the phenomenon poses several legal problems at both practical

and fundamental level. The present research aims to answer a number of remaining legal

questions and to assess mixity from an EU constitutional law perspective, specifically under the

principle of institutional balance: what kind of mixity do we see post-Lisbon? How has the Court’

jurisprudence on the exercise of the EU’ external competences, affecting the question of mixity

evolved post-Lisbon? How should this post-Lisbon mixity be assessed under the principle of

institutional balance enshrined in the EU Treaties?