Introduction. Due to its antisocial and destructive nature, terrorism constitutes a particular threat to the public, national and international security. It is one of the global problems of our time, which leads to the increased tension, has the high conflict potential and extremely negative effect on development and life of a society, a separate state and the globalcommunity on the whole. Cooperation between the national states and the international organisations for combating the international terrorism is most often restricted to the individual cases. In this context, the principles of law, which represent the concentrated essence of the universal values and ideals underlying the legal regulation of the social relationships, become particularly acute and relevant. The present article aims to analyse the theoretical and practical aspects of the principle of legal certainty in counteracting the international terrorism. Materials and Methods. The object of the study is the principle of legal certainty as a tool of counteracting the international terrorism. The dialectical method of cognition was used as the main research method, the general scientific methods of analysis, synthesis and the specific legal methods (empirical and legalistic) were also used. Results. It has been proved that the spread of extremism and terrorism constitutes a threat to the present day international and national legal order. The necessity to formulate a unified general definition of the concept of “terrorism” and to implement the principle of legal certainty in counteracting the international terrorism has been substantiated. Discussion and Conclusion. The research has revealed the need for an optimal and efficient solution for implementation of the non bis in idem (“not twice for the same”) principle with regard to the terrorist crimes (primarily of the international nature), endowing the universal jurisdiction over them, which allows criminal prosecution of the criminals regardless of their location, citizenship or territory, where the individual crime has been committed. The theoretical and practical value of the results obtained is the capacity thereof to be used both in the field of scientific research (for further theoretical study of the problems of counteracting the international terrorism) and in the field of law-making (for improving the Russian Federation legislation on counteracting terrorism). Bearing in mind future research, the special attention should be paid to the optimisation of the legal framework, enhancement of the regulatory legal mechanisms aiming to prevent in an optimal way the international terrorism as a social phenomenon.