Compared to other species, humans are unusual in both our capacity for extensive and cumulative culture and our large, non-kin-based cooperative societies. In this chapter we review recent theories that draw links between these two unusual traits. Theories of indirect reciprocity posit that language allows cooperation to be maintained in human groups through the formation of reputations, and cooperation can also be maintained through altruistic or third-party punishment of noncooperators. The theory of cultural group selection holds that cooperative tendencies arose as a result of competition between internally cohesive cultural groups in human prehistory. We also discuss the role of social emotions in maintaining cooperative societies. Finally, we review recent work that suggests that population size can set limits on the degree of cultural complexity that can be maintained, suggesting a two-way interaction between culture and sociality.