The papers brought together for this special edition serve, collectively, to underline just what a pervasive concept ‘transnational policing’ has become. Moving from a situation, in the not too distant past, where policing was routinely if not always accurately presented as first and foremost a function of the nation state, the last twenty years of research have shown that there now exist important transnational, or cross-border, aspects of police-work – and of police organizations. While police remain a tool of states concerned with controlling the territories they govern – a fundamental aim of all policing efforts – the means, and increasingly ends, of this practice now spill across borders and involve multiple police agencies at international as well as national levels. Two factors seem to have been particularly important in this process, and both are covered in the papers collected here: increasing flows of people, as well as goods and capital, across borders; and the inter-connected rise of information technology and the new forms of surveillance this both enables and seems – to many – to require. Indeed, it may now appear implausible to suggest a state (certainly, a democratic state) could now control its territory without working in conjunction with other state and international actors, not only in terms of maintaining borders and monitoring those who cross them, but also in terms of the need to attend to threats operating within those borders yet which draw on resources distributed at, potentially, a global level.