This chapter deals with the radicalisation of Mohamed Merah, a young man who committed a series of terrorist attacks in France in 2012, in the cities of Toulouse and Montauban. It exposes a family-ecology analysis, with the aim of understanding the intersecting life trajectories of the various members of the ‘Merah clan’. It allows us to identify a series of specific sequences in the life trajectory of Merah but also of other members of the family. A focus is made on the individual and group mechanisms, particularly at the socio-familial level.