The first aim of this paper is to revisit the puzzle of cooperation in large-scale societies.It proposes a game theoretic model showing how endogenous emotion-based punishment can sustain ull cooperation when interactions are not repeated, provided that players' endogenous trust is high enough. The model the signalling theory of religion. Finally, the model enables clear and tractable predictions about the levels of religious affiliation and participation within a society. Evidence of the model's implications is discussed.