Many experts on security intelligence distinguish 'mysteries' from 'secrets'. Mysteries (e.g. can Pakistan survive the threat it faces from the presence of insurgents in its western provinces?) are worldly phenomena that governments may wish to understand, but which are difficult to fathom given the foibles of human beings, not least their inability accurately to foretell the future. Secrets (e.g. the number of nuclear submarines in the Chinese navy), however, are more susceptible to understanding. Indeed, with the right spy in place, with surveillance satellites in their proper orbit, or with reconnaissance aircraft well-positioned in enemy airspace, secrets can be deduced, but governments are largely limited to thoughtful speculation about the planet's deeper mysteries. Either way, prudent states will seek to establish intelligence-gathering agencies to ferret out secrets and help productively to ponder mysteries.

Serious academic work focusing on issues in and around this kind of activity flourishes as never before, and this new four-volume collection from Routledge's Critical Concepts in Military, Strategic, and Security Studies series addresses the need for an authoritative reference work to make sense of a rapidly growing and ever more complex corpus of scholarly literature.

The first volume in the collection is devoted to the core mission of security intelligence-the collection and analysis of global information (the world's secrets and mysteries). Nations take the task of acquiring security intelligence (often regarded as 'the first line of defence') with the utmost seriousness. Considerable resources-upwards of $50 billion per year in the case of the United States-are spent in the hope of avoiding catastrophic surprises such as the events of 11 September 2001. But, in many nations, intelligence agencies have taken on international assignments beyond this core duty, and they also conduct so-called 'dirty tricks'. Volume II collects the most important work to describe and critically evaluate such covert action, which can include attempts to manipulate history through the use of propaganda, political and economic operations, and paramilitary activities.

Intelligence agencies typically play another important role: guarding state secrets and resources from penetration by foreign governments and factions. The third volume of the collection assembles the essential thinking on the business of counterintelligence. Volume IV, meanwhile, brings together the best work on the vital question of intelligence accountability. Who will guard the guards themselves?

Intelligence is fully indexed and includes a comprehensive introduction, newly written by the editor, which places the collected materials in its historical and intellectual context. It is destined to be valued by scholars and students as a vital one-stop research and pedagogic resource.