This article revisits some of the debates and controversies that have arisen between two French intellectuals well known for their work on Islamism, Gilles Kepel and Olivier Roy. Their respective, conflicting theses are examined to highlight how much importance each gives to the ideological factor when it comes to explaining the terrorist acts that have stricken France and claimed hundreds of lives in the past few years. The article focuses on three aspects of Kepel and Roy’s analyses. First, the weight given to ideology as an explanatory factor for these terrorist acts. Second, the role of the IT revolution as a vehicle for radicalizing ideologies. Finally, an examination of the sociological and psychological profile of those who have committed terrorist acts, as each author grapples with the question: are they religious fanatics or criminals? The article hopes to clarify and summarize the theoretical and sociological opposites that separate the analyses of Kepel and Roy.