This chapter offers a critical descriptive account of the affective dimension of fanaticism. In terms of affective psychology, three elements are crucial to fanaticism. First, the fanatic is lovingly devoted to an object or idea he takes to be sacred, and this loving devotion is constitutive of his social identity: it is part of who he (as a member of a specific group) takes himself to be. Second, the fanatic shows a hostile antagonism toward those people who dissent from his sacred value and, in doing so, threaten both his object of passionate devotion and his group’s self-esteem. Finally, the fanatic sympathetically identifies with a group of people (or another kind of object) he takes to be suffering or oppressed. The chapter provides a detailed analysis of each of these three groups of feelings, thereby specifically paying attention to their social constitution. Moreover, reflecting on the social constitution of the phenomenon of fanaticism itself, the author notes some of the limitations of existing understandings of fanaticism, most importantly the fact that as a normative political concept, the definition and application of the concept of fanaticism is itself entangled with power interests.