Nowadays one of the most dangerous phenomena is terrorism in the European Union, which is a kind of political violence and affects the internal security, as well. Therefore – after a short historical review – it is necessary to examine the definition and conceptualization of terrorism in the European Union’s criminal law system and to clear if the legal regulation is common and adequate? With special regard to the fact, that scholars flash the problem, that there is a lack of common definition of terrorism, which arises some problems at global and at the European Union’s level, as well. My treatise shows the mentioned problems in five chapters. In the first chapter is shown the present impact of terrorism in the European Union and after a short historical review (chapter II) is separately presented the definition of terrorism in the European Union’s law system and in the scientific world, showing the disadvantages of the lack of common definition (chapter III and IV). At the end in the conclusion I present some proposals and possible directions of a new regulatory method.