Abstract: Human sociality is enabled by our ability to develop, maintain, and reinforce social norms. While social norms are universal, there is wide variation in the strength of social norms (or tightness) around the globe. In this talk, I will describe theory and research on tightness-looseness in pre-industrial societies and in modern nations and states, discuss the evolutionary and neurological basis of such differences, and describe the implications of the strength of social norms for managing COVID-19.