In recent years European Union (EU) officials and pundits have rarely missed an opportunity to point out that Europe finds itself in an increasingly tense and uncertain geopolitical environment – and that the EU should strive for more strategic autonomy in order to defend its own interests and those of its member states. Some EU member states are then often quick to point out that the EU has no role to play in collective defence and that this responsibility rests squarely and solely with the North Atlantic Treaty Organization (NATO). Still others prefer to stick to a position of neutrality.[1] But despite their different views, all EU member states already have ‘an obligation of aid and assistance by all the means in their power’ in case another EU member state becomes the ‘victim of armed aggression on its territory’: Article 42(7) of the Treaty on European Union (TEU), also known as the ‘mutual assistance clause’.[2]

When the drafters of the Lisbon Treaty incorporated and amended an old article from the dissolving Western European Union (WEU) in 2007, Article 42(7) initially lay dormant. However, in November 2015 France jolted the EU into action by invoking the article for the first time in response to the Bataclan attacks, thereby initiating a discussion about the scope and nature of this article. Now that it was used in response to terrorism, policymakers began to wonder to what extent it would also cover hybrid forms of aggression and cyberattacks. To complicate matters further, already in 2018 some European politicians began to speculate that it could be invoked in response to confrontations with Turkey in the Eastern Mediterranean. The Greek foreign minister openly hinted at this in a letter in 2020, prompting yet more handwringing in Brussels about the possible consequences of one NATO ally invoking an EU treaty article against another.[3]

Even though many EU member states would prefer to keep this article in a form of strategic limbo, some prefer to bring it more out into the open and see it as useful to promote stronger European defence cooperation.[4] It is clear that Article 42(7) is no longer dormant: in May 2020, the Defence Ministers of France, Germany, Italy and Spain called for its ‘operationalisation’[5] and the EU committed itself to ‘test it out’ during a series of exercises. It also features in discussions on the EU’s Strategic Compass, which are to be finalised under the auspices of the French Presidency of the EU in early 2022. This raises questions as to how a treaty article that as an ‘ultimo ratio’ is rarely meant to be invoked could potentially be operationalised, which strategic considerations should be taken into account, and to what extent this rather traditionally worded Article could also cover modern phenomena such as hybrid threats or cyberattacks.

These discussions take the EU into territory that is both largely unknown and, for many, quite uncomfortable. This report aims to inform these deliberations. Chapter 2 will briefly set out the historical and legal context of Article 42(7) and in particular its relationship to other articles of the EU Treaties, the North Atlantic Treaty and the United Nations (UN) Charter. Chapter 3 will explore its applicability to a number of potentially contested areas that may become of relevance in the future, including cyberspace, space itself and the maritime domain. Based on this analysis Chapter 4 will put forward three sets of situations in which the article could be invoked in the future and illustrates these with brief hypothetical scenarios. Chapter 5 will map out the different opinions and interpretations of EU member states and will set out the procedural and institutional aspects. This includes the potential involvement of the EU institutions, despite the strictly intergovernmental and member state-driven character of the article. It concludes with a set of policy recommendations for the Government of the Netherlands and the EU as a whole.

The research is based on a combination of a review of publicly available literature and a series of interviews with representatives of EU institutions and member states. The report also includes three external contributions by experts from France, Finland and Cyprus, who each explore the strategic considerations of their respective countries and focus on particular dimensions of Article 42(7) that are relevant to their own security context. The authors would like to thank Elie Perot, Dr. Teija Tiilikainen and Dr. Constantinos Adamides for their valuable contributions, which have also informed the analysis of the main report and have been included in its annexes. The views of the external contributors remain exclusively their own.

For an overview see Dick Zandee, Bob Deen, Kimberley Kruijver and Adája Stoetman, “European Strategic Autonomy in security and defence: Now the going gets tough, it’s time to get going,” Clingendael Report, (The Hague: December 2020).
In publicly available literature and EU documents the article is referred to as both the ‘mutual assistance clause’ and the ‘mutual defence clause’. While strictly speaking the choice of reference to the article has no legal consequence, this report will use the term ‘mutual assistance clause’ to highlight its differences from the collective defence clause in Article 5 of the North Atlantic Treaty.
See for example the written questions by the Member of the European Parliament Eleni Teocharous to the European Commission entitled “Recent provocative moves by Turkey calling into question the sovereign rights of Greece and Cyprus — Implementation of the Treaty of Lisbon — Article 42(7),” Question number P-001956-18, (30 March 2018); and the Letter of Nikos Dendias to Josep Borrell, (19 October 2020).
Anne Bakker, Sven Biscop, Margriet Drent and Lennart Landman, “Spearheading European Defence: Employing the Lisbon Treaty for a Stronger CSDP,” Clingendael Report, (The Hague: September 2016).
Letter of the Ministers of Defence of France, Germany, Spain and Italy to Josep Borrell,” (29 May 2020), which includes “Another lesson we collectively identified is the importance of European solidarity to act and react to crises. A key work, in that regard, will be the operationalisation of the Article 42(7) TEU.