This article not only studies the cooperation between the European Union (EU) and Association of Southeast Asian Nations (ASEAN) in the fight against terrorism but also shows the interactions between the fight against terrorism within the EU and within ASEAN. It starts with an analysis of EU's and ASEAN's respective terrorist threats and a comparison of the EU and ASEAN as counterterrorist actors. Regional cooperation within ASEAN is still at its infancy stage, as ASEAN is profoundly attached to the principles of state sovereignty and non-interference, whereas the EU has developed a real strategy in order to pursue and prevent terrorism. Thus, the EU has been brought to integrate its fight against terrorism into all aspects of its foreign policy and has recognized that south-east Asia is a critical factor for its security agenda. Inter-regional cooperation is slowly emerging, notably through the ASEAN Regional Forum and the Asia-Europe Meeting.