It is almost certainly a clich é by now that the September 11, 2001, terrorists attacks on the United States changed the world. These events did so in many ways, including the launching of a multinational war in Afghanistan against al-Qaeda. But perhaps the most significant change was in the eroding of the traditional boundaries between domestic policing and criminal justice and international security concerns. In countries such as the United States, Great Britain, and Spain, three countries that experienced terrorist attacks, political and legal pressures were placed on the government to protect the borders, maintain law and order, and also respect domestic and international human rights and law. But well before the events of 9/11 and the appearance of al-Qaeda on the international scene, other countries faced what they considered to be domestic terrorist or other threats that challenged the capacity of law enforcement agencies to respond. This included Great Britain and its effort to address violence and unrest in Northern Ireland inspired by Republican or Loyalist forces in Belfast. How the American and British authorities and the police responded to their threats is the subject of Preventing Ideological Violence: Communities, Police and Case Studies of “Success,” , edited by P. Daniel Silk, Basia Spalek, and Mary O’Rawe.