Terrorism constitutes a major threat to security in the European Union. Horrific terrorist attacks since 2015 have killed and injured hundreds of innocent people and have left many more in shock and grief. Prosecutors and investigative judges play a key role in tackling terrorism. They are the guarantors of a lawful criminal justice process and have a central operational role right from the start of the investigation: they often lead the investigations, ensure coordination across national borders, plan and instruct the police to arrest suspects and collect evidence, define the prosecution strategy and finally bring the suspects before a court of law. Eurojust, the EU Agency for Criminal Justice Cooperation, operating from The Hague, is a unique hub where national judicial authorities get hands-on support to work together in the fight against serious cross-border crime, including terrorism. Each Member State has a National Member at Eurojust and can use various forms of practical assistance to enable efficient collaboration in criminal investigations and to promote the development of crucial expertise.