The roots of organized crime penetrate deep into the normal operations of society, its economic and financial patterns, sometimes also its bureaucracy and ideological apparatuses. Drug trafficking, traffic in persons or terrorist networks could not exist if they did not engage large groups of people and routine patterns of social and economic behaviour. Often the “indirect” actors remain hidden, however, and beyond the reach of the arm of the law. In an analogical way, “terrorism” emerges from and is sustained by a wide network of ideological, economic, financial and other actors and activities. Marja Lehto maps in this work the way in which international legal regulation, particularly the new conventions adopted within the UN after 1996 ,have sought to extend international responsibility beyond the groups of immediate perpetrators, to the sources or incitation, recruitment, and financing of terrorist activities.She also deals with some of the thorniest questions in the field along the way – from the significance and difficulties in the of efforts to define “terrorism” to the need for a “general part” of international criminal law, and the role of a political organ – the United Nations Security Council – in preventing and punishing the crime of terrorism..This carefully crafted, insightful and hugely relevant study not only fulfils a gap in the existing literature but does so with analytical precision, bearing simultaneously in mind the important political and theoretical, even philosophical implications of this contentious topic. “Few topics have generated more international law writing in recent years, both scholarly and polemical, than terrorism. [...] So it is a genuinely welcome surprise when someone brings out a study that has a fresh angle on the topic, and all the more so if the writer not only fulfils what appears like an obvious gap in existing literature but does that with analytical precision, bearing simultaneously in mind the important political and theoretical, even philosophical implications of this contentious topic. This is what Marja Lehto does in this carefully crafted, insightful and hugely relevant study of what she suggests we call ‘indirect responsibility’ for terrorist acts.” Martti Koskenniemi, Academy Professor (University of Helsinki)