1 “ INTRODUCTION Historically, citizenship has rarely been considered an unconditional entitlement. Banishment was practiced quite widely across Europe until the 1800s, and throughout the 20th century most Western states had laws enabling loss of citizenship for treason or its equivalent. The laws on deprivation that have emerged over the last two decades often modify and update old laws rather than create entirely new powers. That said, denationalisation as a practical instrument of state virtually disappeared in the West after 1945, not least because citizenship stripping was de-legitimised by association with totalitarian regimes. In practice if not in law, then, citizenship became widely understood as unconditional status and the logic of citizenship in the West was overwhelmingly one of rights rather than obligations”.1 In recent years, a new chapter has been added to the story that is captured by this quote, as nationality deprivation enjoyed a remarkable resurgence of interest – repackaged for the 21st century as a counter-terrorism instrument. The media frenzy around a handful of citizenship stripping cases, such as that of Shamima Begum, Jack Letts and Suhayra Aden, has further fuelled heated political debates about the use of stripping citizenship. Proponents draw on a powerful rhetoric of symbolism and belonging to make their case that citizens who have aligned themselves with international terrorist groups can no longer be part of the political community. As deprivation powers in the United Kingdom were expanded and an increasing number of citizens were targeted for denationalisation, the Home Office remarked that “citizenship is a privilege, not a right”.2 Critics challenge the legitimacy of this use of government power and point to a ream of contemporary international law obligations that should constrain its use; while also questioning the wisdom of ‘dumping’ these unwanted citizens in volatile and unmonitorable places like North Syria, expressing concern at the longer-term security implications of this strategy. Successive UN Security Council Resolutions call for the cooperation of states in “the fight against terrorism”3 and “efforts to address the threat posed by foreign terrorist fighters”.4 Stripping people of their nationality for the stated reason of national security and subsequently expelling them to another state is contrary to this duty of cooperation. Moreover, both the UN General Assembly and the UN Security Council have noted on various occasions that states are under an obligation to bring terrorists to justice under the principle to “extradite or prosecute” (aut dedere aut judicare).5 Whenever states, by means of depriving a person of their nationality, expel known terrorists from their territory, they fail to investigate and punish terrorist action. By expelling (suspected) terrorists, states also lose effective control over those individuals, which has been recognised to significantly complicate the monitoring and prosecution of terrorists. Such exporting of risks is at odds with durable, global security,6 while also violating the sovereignty and territorial integrity of the other state.7 The use of deprivation of nationality on the pretext that it serves national security aims has garnered significant attention and much has been written about it, but just how widely has this measure been adopted? This report offers the first comprehensive global survey of relevant legislative provisions, covering 190 countries – discussing the prevalence and scope of these powers (Section 2), as well as questions such as who has the authority to take deprivation decisions, which citizens can be targeted by for denationalisation and can it result in statelessness (Section 3). 6 THE PRINCIPLES ON DEPRIVATION OF NATIONALITY AS A NATIONAL SECURITY MEASURE Published in March 2020 and enjoying the endorsement of numerous leading international experts, these Principles provide an authoritative overview of existing international law obligations and apply to all situations in which States take or consider taking steps to deprive a person of nationality as a national security measure. The Principles set out the basic rule that “states shall not deprive persons of nationality for the purpose of safeguarding national security”. Any exercise of an exception to this rule, must be “interpreted and applied narrowly, and only in situations in which it has been determined by a lawful conviction that meets international fair trial standards, that the person has conducted themselves in a manner seriously prejudicial to the vital interests of the state”, and is further limited by other well-established standards of international law. Further details in Section 5 of this report. The report also encompasses a longitudinal study of how deprivation powers have evolved since the year 2000 – i.e. after the 9/11 terrorist attacks in the United States and during the period marked by the rise and fall of ISIS (Section 4). To achieve this, the laws in force on 1 January 2000 are compared to those on the books on 1 January 2022, with a view to identifying where grounds for deprivation have been introduced and repealed, expanded and narrowed. A brief discussion of the use of nationality deprivation in practice is included in this section of the report, offering some insights into available data as well as a number of individual cases that help to reveal the variety of “outcomes” that follow after denationalisation. The report also looks at how we should understand the evolving use of citizenship stripping in light of contemporary international law standards (Section 5). International law protects the