Introduction. The article deals with a number of theoretical issues related to the development and content of the basic methodology of investigation of organised forms of criminal activity of extremist orientation. The attention is emphasised on the twocomponent vector of scientific and methodological support in the aspect of supplying the subject of investigation with forensic methods and techniques of investigation. The technological features of the implementation of the mechanism of criminal activity of extremist formations are analysed. It is concluded that the last ones naturally predetermine the complexity of investigative activity in cases of this kind. The objective necessity of formation of the basic (enlarged) methodology of investigation of extremist crimes committed in organised criminal forms is proved. The criteria for the development of criminalistic characteristics as an information basis for the creation of complexes of methodological recommendations are studied, the elements for inclusion in the content of the considered methodology are proposed. Special attention is paid to typical criminal situations and accompanying sources of information about the criminal event, as well as recommendations for the formation of initial forensically significant information. Methods. The methodological basis of the research is the universal dialectical method, the application of which led to the analysis of objective reality related both to criminal activity of extremist orientation, committed in organised forms, and to the activities of law enforcement agencies in its investigation. The author used methods of comparative and system-structural analysis, synthesis of structural elements of investigative activity in cases of this kind, modelling of the process of formation of initial forensically significant information in relation to typical sources of information about such a criminal event. Results. It is obvious that given the complexity of the mechanism of implementation of the considered type of criminal activity, investigative tasks cannot be effectively solved without proper scientific and methodological support of the investigative process. This situation determines the need for scientific comprehension and formation on its basis the results of the conceptual foundations of the basic methodology of investigation of crimes committed by extremist formations.