The purpose of this contribution is to propose solutions in the event that an EU Member State activates the withdrawal clause of Article 50 TEU. To this end, the authors analyse international and European Union law perspectives with regard to the recent practice relating to Brexit. As is well known, Article 50 TEU provides for the conditions and consequences of the withdrawal of a Member State from the EU. However, it is silent on the participation of the withdrawing state in mixed agreements. Firstly, EU-only treaties cease to apply on the date on which a Member State withdraws from the EU. Secondly, several mixed agreements contain a territorial application clause limited to the territories of EU Member States and corresponding third parties (neither of which correspond to the departing state). In these circumstances, although the UK may formally remain a party to such agreements under international law, such agreements would in practice cease to apply to it. As a matter of fact, the UK concluded new agreements with third countries. It replicated, as far as possible, the effects of the EU's trade arrangements with partner countries, as they were applied to the UK through mixed agreements prior to the end of the transition period. (source: book's introduction, p. 17-18)