In the first half of the 1980s a succession of high profile and deeply controversial trials took place in Northern Ireland on the evidence of 'supergrasses' from loyalist and republican paramilitary organisations prepared to betray large numbers of their former alleged confederates in return for immunity from prosecution or lenient sentences and new identities outside Northern Ireland. This, the first thoroughly-researched book-length study of this process, not only carefully documents the central trials - some of which were larger than any other criminal proceedings in the UK or Ireland - but also opens a rare window on the highly secret world of the terrorist groups concerned. The origins of the supergrass system are traced through the complex web of intelligence gathering and counter-terrorist policy in Northern Ireland, and the broader criminal justice and criminological issues are fully explored. The author also compares and contrasts the failure of the supergrass experiment in Northern Ireland with its much more successful counterparts in England, the United States, Italy and Germany, and considers why France and Spain chose not to go down the supergrass path. The publication of this book could hardly be more timely. Northern Ireland is once again at the top of the political agenda in the United Kingdom and Ireland, and the recent ceasefires have ensured that the Troubles are the focus of renewed international attention. The need for strong due process rights in the criminal justice system as part of an overall settlement of the Ulster conflict is firmly underlined, and the study adds further support to the case for more effective mechanisms of public accountability over policing and intelligence-gathering in liberal democracies generally.