On the afternoon of September 11 2001 the Irish Prime Minister (Taoiseach), Bertie Ahern ordered the ‘heads of the security services of key government departments’ to undertake a complete re-evaluation of measures to protect the state from attack. Hence, underway within hours of the 9/11 outrage in the United States was potentially the most far-reaching review of Irish national security in decades. This book, the first major academic investigation of Irish national security policy as it has operated since 9/11, provides a theoretically informed analysis of that re-evaluation and the decisions which have been taken as a consequence of it up until September 2008. In so doing it draws on unprecedented access to Ireland’s police, security and intelligence agencies; over twenty senior personnel agreed to be interviewed.Theoretically the author demonstrates the utility to the analysis of national security policy of three conceptual models of historical institutionalism, governmental politics and threat evaluation. The text is of interest to scholars of Security Studies, International Relations and Politics, as well as state and NGO personnel, journalists and general readers.