This article examines the concept of terrorism as a social and legal phenomenon, its international legal and criminal-legal characteristics. Highlighted are the main aspects of cooperation of the states and the international community to counter terrorist activities. Terrorism as a social phenomenon is determined by paragraph 1 of article 3 of the Federal law of 06.03.2006 No. 35-FZ "On combating terrorism" according to which terrorism is understood under the ideology of violence and practice of influence on decision-making by public authorities, local self-government bodies or international organizations connected with frightening the population and (or) other forms of unlawful violent actions. Thus, terrorism is a social phenomenon that has many criminal legal forms of manifestation--specific elements of terrorist crimes. [For the complete Volume 15 proceedings, see ED574185.].