It is not uncommon for states, including many liberal democracies, to deport foreign nationals present on their territories who engage in extremist behaviour. In this article, we argue that such extremist deportations are sometimes justified. We identify four important goals that such deportations may serve: (i) protecting the stability of liberal-democratic regimes; (ii) protecting the basic rights and liberties of citizens and (remaining) non-citizen residents; (iii) communicating a state’s liberal-democratic commitments; and (iv) reassuring citizens and non-citizen residents whose basic rights and liberties are being challenged by extremists that the state will safeguard their freedom and equality. We also answer three objections to the practice of deporting non-nationals based on their extremist acts, namely that his practice (I) is vulnerable to political abuse; (II) imposes disproportional costs upon the deported; and (III) produces unfairness towards the societies that must accept them back. We argue that these objections fail to show that such deportations are categorically unjustified, but we do impose various conditions on the moral permissibility of extremist deportations in response to them. We conclude that the practice of deporting extremists is morally justifiable if and only if they have been found guilty by a criminal court of (at least) one of an exhaustive and public list of deportable extremist offences; the costs that are imposed upon the deportee and possible loved ones are proportional to the protective and communicative functions served by such deportations; and fairness towards receiving countries has been ensured.