The article is aimed to characterize the role of famous Russian orientalist G.I. Mirsky in defining and distinguishing categories related to the increasing influence of Islam on politics. Such concepts as "islamism", "fundamentalism", etc., came into academic science from polemical texts, expert assessments, and analytics. The work carried out by G.I. Mirsky to identify their meanings and clarify the content made it possible to introduce these categories into scientific framework, and therefore to give a more accurate evaluation of the most important political events, to classify the actions of various political actors, to predict their behavior. The article is aimed to characterize the role of famous Russian orientalist G.I. Mirsky in defining and distinguishing categories related to the increasing influence of Islam on politics. Such concepts as "islamism", "fundamentalism", etc., came into academic science from polemical texts, expert assessments, and analytics. The work carried out by G.I. Mirsky to identify their meanings and clarify the content made it possible to introduce these categories into scientific framework, and therefore to give a more accurate evaluation of the most important political events, to classify the actions of various political actors, to predict their behavior.