The article covers the phenomenon of Islamist terrorism in the countries of Western Europe. The key research method is interdisciplinary approach. The multidimensional nature of the phenomenon under consideration, which is related to the spread of radical trends of political Islam among a certain part of the European Muslim community, particularly among young people, and also to double standards in the politics of Western countries towards radical Islamism in the Arab Muslim region, is analyzed in details. On the one hand, Western countries fought against Islamist movements, whose actions were in conflict with the interests of the West in Afghanistan and the African Sahel, but, on the other hand, they supported Islamist «rebels» and tried to use them for their own purposes in order to remove «unwanted» regimes in Libya and Syria. The results of such politics, that has given rise to radical Islamism and ISIS and their expansion in Iraq and Syria are revealed. The main aspects of «jihadist» ideology, the influence of which has led to the intensification of Islamist terrorist activity, are examined. The particular attention is paid to the internal situation in the European Arab Muslim society on the example of its largest community in France. The difficult social and economic problems aggravated by the COVID-19 pandemic and affecting primarily the Muslim-migrant community (especially its youth segment), are exposed. They became most important factors in the radicalization of the part of Muslim community. The activities of numerous Muslim organizations reflecting the interests of various ethnic groups and trends in Islam are examined thoroughly. The role of Islamic factor which became the integral element of the social and cultural landscape of French society is analyzed. Also, it is exposed that a part of French society does not accept this reality. The author concludes that the problem of combating the Islamist threat is complex and diverse. Western society cannot adequately respond to this challenge.