Implementing Article 42.7 of the Treaty on European Union: Legal Foundations for Mutual Defence in the Face of Modern Threats

Following the terrorist attacks in Paris in November 2015, the French government invoked Article 42, paragraph 7, of the Treaty on European Union – the Union’s “mutual defence clause”. Invoking this clause was legally complex, as it not only called into question the meaning and scope of the clause itself but also raised questions regarding the mechanisms for application and the obligations it imposed on the other Member States of the European Union (EU). Moreover, the invocation sparked new interest in the clause itself and has renewed debate between the Member States and within the European Union’s institutions as to its use, scope and (lack of) procedural aspects.