Confessional affiliation is often associated with dialectal difference in the modern Arab World. How do such religion-related differences arise, and what factors maintain or erode them? It seems that ‘confessional varieties’ originate historically as geographically based speech differences, acquiring new social meanings as a result of population movements, whether economically motivated, or caused by force majeure. But such social ‘indexicalisation’ of speech difference does not arise, nor is it maintained, automatically or even in every case: that is determined by long-term patterns of inter-communal contact. Two case studies are presented in this chapter: Baghdad and Bahrain.