Great strides have been made over the last several decades in understanding values across cultures, yet there has been little systematic attention to cultural variation in social norms. In this presentation, I will focus on a neglected dimension of culture, namely differences between nations that are ‘tight’–have strong norms and high sanctioning of deviant behavior – versus ‘loose’– have weak norms and low sanctioning of deviant behavior. Early anthropological research showed the promise of this distinction in traditional societies (Pelto, 1968) and our research illustrates the importance of this distinction in modern nations. Situating our work within an eco-cultural framework, we found evidence that tightness-looseness is afforded by a broad array of ecological and human-made societal threats (or lack thereof) that nations have historically encountered. Ecological and human-made threats increase the need for strong norms and sanctioning of deviant behavior in the service of social coordination for survival, whether it is to reduce chaos in nations that have high population density, deal with resource scarcity, coordinate in the face of natural disasters, defend against territorial threats, or contain the spread of disease. Nations with few ecological and human-made threats have a much lower need for social coordination, affording weaker social norms and much more latitude in what is considered appropriate behavior. We also illustrate how tightness-looseness is implicated in broad versus narrow socialization in societal institutions (autocracy, freedom of the media, criminal justice systems) (Arnett, 1995), the strength of everyday situations (Mischel, 1977), and psychological processes that simultaneously support and reflect the strength of norms and sanctioning in the larger societal context. Field, experimental, and computational research will be discussed.