The terrorist attacks that have been haunting European capitals show us that counterterrorism is necessary and essential in modern day society. The intelligence services and other organisations active in the field of counterterrorism are faced on a daily basis with the question of how extensive and intrusive their actions can be. What are the limits? Which actions are ethical? And most importantly: how do the professionals themselves deal with these - often complex - dilemmas? In Ethics of Counterterrorism scientists, counterterrorism agents and ethicists reflect on this theme and discuss many urgent questions.