We conducted a large-scale survey covering 58 countries and over 100,000respondents between late March and early April 2020 to study beliefs andattitudes towards citizens’ and governments’ responses at the onset of theCOVID-19 pandemic. Most respondents reported holding normative beliefs insupport of COVID-19 containment measures, as well as high rates of adherenceto these measures. They also believed that their government and their coun-try’s citizens were not doing enough and underestimated the degree to whichothers in their country supported strong behavioral and policy responses to thepandemic. Normative beliefs were strongly associated with adherence, as wellas beliefs about others’ and the government’s response. Lockdowns were asso-ciated with greater optimism about others’ and the government’s response, andimprovements in measures of perceived mental well-being; these effects tendedto be larger for those with stronger normative beliefs. Our findings highlighthow social norms can arise quickly and effectively to support cooperation at aglobal scale.