The purpose of this introductory chapter is to give an overview of why intelligence cooperation has come to prominence post-9/11 and to introduce the main accountability, legal and human rights challenges that it poses. International cooperation between national security and intelligence services presents the most significant oversight challenge in the field of national security today. It hardly needs stating that intelligence and security agencies primarily exist to protect and further the national security interests of states. Since the end of the Cold War, however, the threats which national services tackle have become increasingly transnational in nature. The acceleration of globalisation has contributed to the expansion in scope and span of networks engaged in – amongst other things – organised crime, the proliferation of weapons of mass destruction and terrorism. The growth of these transnational threats has impelled intelligence services to cooperate with counterparts in other states in order to meet these challenges. Cooperation between selected Western states and in certain areas of intelligence operations (such as signals intelligence) is longstanding. Since 9/11, however, there has been an exponential increase in the both the scope and scale of intelligence cooperation, including that between formerly non-aligned and hostile states. In particular, the fight against international terrorism has provided the rationale for a dramatic increase in multilateral and bilateral intelligence cooperation. The scale of this collaboration has increased in terms of the volume of information shared and the number of joint operations. At the same time, the scope of intelligence cooperation has broadened to include a greater range of states (particularly non-traditional allies in the Middle East and Asia) and a wider variety of intelligence activities. These widening and intensified cooperation activities represent a growing challenge to accountability. As has been widely documented, certain manifestations of intelligence cooperation have led to high-profile controversies, such as the revelations about the extraordinary rendition,

interrogation and secret detention of suspected terrorists. However, in a sense, these are the tip of the iceberg. International cooperation has in general evaded the scrutiny of national oversight and review structures, which were designed for a different era, and in response to a very different set of abuses. Indeed, it has become increasingly evident that these bodies are ill equipped to hold intelligence services and their political masters to account for their cooperation activities. While both the threats to national security and the responses to these threats have become increasingly “globalised”, accountability mechanisms have remained territorially bounded. The growing cooperation between national intelligence and security agencies has not been matched by international collaboration between national oversight and review bodies. Ultimately, the combination of the weaknesses of these bodies on the one hand, and the levels of secrecy, sensitivity and multi-territoriality inherent in international cooperation activities on the other, has led to an increasing accountability deficit.