On 17 November 2015, France invoked for the first time article 42(7) or the mutual assistance clause (mutual defense clause) of the Treaty on the European Union (TEU), asking for aid and assistance from the other European Union (EU) Member States in the aftermath of the deadly terrorist attacks in Paris on 13 November 2015.
Included in the European Union primary law in 2009 by the Lisbon Treaty, under the specific provisions on the Common Security and Defence Policy (CSDP), the EU mutual assistance clause (or the EU mutual defence clause as it is called by many), has never been used so far.
France’s decision to request assistance from the other Member States under article 42(7) TEU over other possibilities has been explained in various ways, not least through the preference of dealing bilaterally with the other EU governments, without involving the EU institutions.
All EU Member State have unanimously promised their full aid and support for France, but the process of concretely defining their commitments is still ongoing. (http://www.europarl.europa.eu)