The perceived surge in external threats such as hybrid and cyber warfare, the instability in EU neighbourhood, and deadly attacks on the very EU territory, jointly with the pending process of the UK leaving the European Union, recently renewed political and academic interest in the establishment of a European Defence Union (EDU). EDU is foreseen in Article 42(2) Treaty on the European Union (TEU), as part of Common Security and Defence Policy, but only with Resolution of 22 November 2016 the European Parliament called for its establishment.
While the project is still at its embryonal stage, in the view of the European Parliament the EDU is likely to encompass a permanent structured cooperation and an own fund. The permanent structured cooperation is a mechanism for MSs to combine their military efforts provided for in the TEU, but never implemented or used until now. The opportunity to use a start-up fund is also foreseen in the TEU, Article 41(3). This article devotes attention to the legal foundations of EDU. In discusses issues related to its establishment, functioning, aims, and funding; in addition, it explores the relationship between EDU and other options available to policy-makers for providing a European defence: the mutual defence clause of Article 42(7) TEU and the mutual assistance clause of Article 222 Treaty on the Functioning of the European Union.