This paper explores the leading role that ideas and beliefs can play in the formation of groups and their political action, with particular reference to the psychology of groups and movements involved in genocide. The paper asserts the notion of the Idea as leader; thus moving away from Freud's more limited notion in “Group Psychology and the Analysis of the Ego” of the leader as a person, a charismatic figure generating feelings of love and attachment. Alluding to the work of Bion, Neri and Anzieu, the paper examines the political and psychological significance — the willed quality — of group phantasy in group-initiated mass murder, from Nazi genocide to the ideology of radical Islamic terrorism.