In response to the terrorist attacks of 11 September 2001, the United States embarked on a dramatic and sustained effort to reform and revitalize its homeland security policies and structures. This book offers an examination of the evolution of policy and the concurrent restructuring of existing agencies, as well as the creation of new bodies designed to counter the threat of transnational terrorism. Detailing the historical roots of US homeland security policy and its evolution in the aftermath of the 9/11 attacks, this book provides a unique overview of the emerging and existing agencies and bureaux at the national, state and local levels which are tasked with homeland security. Furthermore, by integrating the existing paradigms of contemporary security policy with the changing nature of threat and response, it provides an invaluable overview of existing and likely future security threats to the US homeland.