Introduction - In the context of the COVID-19 pandemic, as soon as the government announced the lockdown on March 17, Santé publique France established a surveillance system to monitor the public’s adoption of preventive measures. The objective was to estimate the level of adoption of the preventive measures recommended by public authorities according to population characteristics (sociodemographic factors, living conditions related to the COVID-19 pandemic and the lockdown), to identify associated cognitive and affective factors (perceptions and knowledge), and to track changes in these factors during the lockdown period. Methods - Independent samples of 2,000 people aged 18 and older, residing in metropolitan France, were surveyed online. The data presented are from five survey waves. A total of 10,013 individuals were surveyed between March 30 and May 6, 2020. The primary variable of interest was the number of measures systematically adopted out of the 7 recommended by public authorities. The explanatory variables were grouped into three distinct blocks: 1/ sociodemographic variables; 2/ living conditions related to the COVID-19 epidemic and lockdown; 3/ cognitive and affective variables. To quantify the strength of the link between the number of measures consistently adopted and the explanatory variables, multiple linear regressions—adjusted for gender, age, socioeconomic status, and survey waves—were performed. Results - During the lockdown period, the French adopted a high number of preventive measures, regardless of population profiles, with an average across the five survey waves of more than five measures systematically adopted out of the seven recommended by public authorities. Differences across population profiles were observed. Men, younger individuals, those in lower socioeconomic classes, the economically inactive, people with lower levels of health literacy, those reporting that they continued to work outside the home, and those who did not have a close contact who exhibited symptoms related to COVID-19 adopted, on average, fewer preventive measures. During the lockdown period, the number of measures consistently adopted decreased. The consistent adoption of these measures was primarily explained by cognitive and affective determinants: the three main ones were subjective norm (approval and adoption of measures by close contacts), perceived ability to adopt the recommended measures, and, to a lesser extent, perceived severity of the disease.Conclusions - To encourage the adoption of preventive behaviors by the population, our data suggest prioritizing the reinforcement of social norms for adopting these behaviors and individuals’ capacity to implement them. To achieve this, it will be important to communicate clearly and simply about the modes of virus transmission and preventive behaviors, and to create opportunities within the physical and social environment to facilitate their adoption (access to protective equipment, organization of physical distancing, etc.). Following a social marketing approach, the communication strategy would benefit from promoting a social norm of adopting preventive measures for oneself and for others, targeting young adults and men in particular.