Instances of cross-border use of force against non-state actors are not new, but what is new is their frequency and intensity, particularly after 9/11. The book under review examines the legal framework that applies to such use of force. More specifically, it considers the relevant jus ad bellum, jus in bello, and human-rights rules that apply to such actions. The book is thus divided into three parts, each examining one of the aforementioned legal frameworks. The concluding chapter summarizes the author's main findings and applies them to specific cases such as the Israel–Hezbollah conflict of 2006 and the targeted killings of individuals in Yemen and Pakistan.

Concerning the jus ad bellum framework, the author follows the conventional view that a state can use force by way of self-defence against an armed attack mounted by another state and that self-defence also extends to cases in which an attack is imminent but not when the attack is just speculative. As far as non-state actors are concerned, the author's contention is that a state can act in self-defence against non-state actors located in the territory of another state only when the host state is unwilling or unable to take effective measures against them (Chapters 1 and 2). For the author, any use of force other than in self-defence such as the use of force by way of reprisals is prohibited by international law (Chapter 3). However, this rather restrictive view is tempered by two things: (i) the lack of precise definition of what constitutes an armed attack and (ii) the author's admission that a different threshold may apply to armed attacks by non-state actors compared to armed attacks by states, without, however, indicating what that threshold is (p. 51). As a result, it seems that, by default, the author accepts a rather flexible right of self-defence.

The author then goes on to distinguish his theory of extraterritorial use of force from the theory of extraterritorial law enforcement put forward by Dinstein (pp. 74–80).Footnote ¹ According to this theory, by taking forcible action against terrorist and armed bands, the acting state enforces international law to the extent that the host state is unable or unwilling to reign in the activities of such actors. The difference between Lubell's theory of extraterritorial use of force and that of extraterritorial law enforcement is, however, semantic because, according to Dinstein, extraterritorial law enforcement is indeed a form of self-defence, albeit no further explanation for such a statement is provided.

Be that as it may, what is missing from an otherwise detailed analysis of the use-of-force regime is any discussion of its relationship with the law of state responsibility. Such a discussion should have touched upon the issue of whether the use of the attribution criteria found in the law of state responsibility to attribute armed attacks to states is legally and practically appropriate. It should also have considered in more detail the application of the circumstances precluding wrongfulness found in the law of state responsibility to uses of force outside the jus ad bellum framework of self-defence. For example, can an act of use of force not amounting to self-defence but satisfying the criteria of necessity be excused? The author conflates the two by saying that the conditions supporting a plea of necessity are the same as those supporting self-defence (pp. 70–1). Still, this does not answer the question of how acts of use of force that fall below the armed-attack threshold − in whichever way such a threshold is defined − will be treated legally. That said, the more theoretical question is, of course, whether the conflation of the law on the use of force and that of international responsibility is methodologically and conceptually justified.

As far as the application of international humanitarian law to extraterritorial operations is concerned, one of the most intriguing questions concerns the categorization of the conflict. According to the author, there are situations in which the law of international armed conflict may apply, particularly when the attack is attributed to the territorial state but, in most situations, the law of non-international armed conflict applies, particularly when the non-state actor acts independently of the host state (Chapter 4). For the author, these two models – international and non-international armed conflict as known from international humanitarian law – can also accommodate new forms of conflict, such as the ‘war on terror’ if the respective conditions are fulfilled. That said, when it comes to the scope of the applicable rules, there are overlaps between the law of international armed conflict and the law of non-international armed conflict, which is a positive development, since it provides more protection to human beings, particularly in non-international armed conflicts (Chapter 5).

Determining the status of individuals caught in such operations and, more specifically, whether they are combatants or civilians is critical because it determines whether individuals should be protected or targeted. Equally critical is the question of what constitutes direct participation in hostilities because that is the situation in which civilians lose their protection under international humanitarian law. Is direct participation in hostilities determined by the civilian's individual actions or by her continuous membership of a group? If it is determined by individual action, which acts amount to direct participation to hostilities and what is the temporal duration of such participation? The author provides a critical overview of the merits and drawbacks of different approaches to the concept of direct participation in hostilities, including the ICRC's interpretative guidance (pp. 147–55) but he does not take sides or make any specific proposals. Instead, he seems to appeal to some future codification of this area. However, such codification will not come as a deus ex machina, but as a result of doctrinal and other debates to which the author's views would have made a valuable contribution.

The third part of the book deals with the application of human rights to extraterritorial operations. When no armed conflict exists, human-rights law applies to such operations, which means that the human right to life, the prohibition of torture, and the freedom from arbitrary detention apply to extraterritorial actions such as killings, abductions, or torture. As far as the use of lethal force is concerned, it is regulated by the human-rights law-enforcement paradigm, which means that it can be justified if it is necessary to achieve a legitimate objective, if it is a measure of last resort, and if it is proportional. In addition to this, the careful planning of the operation as well as the establishment of the facts if the operation results in individual deaths are part of the law-enforcement paradigm (pp. 169–78). A jurisdictional issue that may affect the application of human rights to such operations is the question of whether human rights can apply extraterritorially. According to the author, human rights apply extraterritorially when the state exercises effective control over a territory or over individuals that includes in the latter case control over diplomatic and consular premises or detention facilities, or direct personal control (Chapter 8). In situations of armed conflict, the author follows the, nowadays, prevalent view that international humanitarian law applies concurrently with human-rights law. Yet, the author admits that uncertainty with regard to certain humanitarian rules, for example with regard to the definition of direct participation in hostilities, causes problems in the application of the respective human-rights rules (pp. 236–47).

Overall, the book contains a thorough, detailed, and accomplished discussion of the law that applies to the extraterritorial use of force against non-state actors. However, the law in many respects is unsettled; therefore, what the present reviewer would like to have seen is the author's considered opinions and arguments on many of the contentious legal issues exposed in the book. This would have definitely helped to move the debate forward.