A large body of research suggests that extraversion is positively related to well-being. However, it is unclear whether this association can be explained by social participation (i.e., more extraverted individuals engage in social interactions more frequently) or social reactivity (i.e., more extraverted individuals profit more from social interactions) processes. Here, we examined the role of social interactions for the extraversion-well-being relationship during the COVID-19 pandemic, an unprecedented time of reduced social contact. We analyzed data from an international, longitudinal study (Study 1: 10,523 assessments provided by 4,622 participants) and two experience sampling studies (Study 2: 29,536 assessments provided by 293 participants; Study 3: 61,492 assessments provided by 1,381 participants). Preregistered multilevel structural equation models revealed that extraversion was robustly related to well-being, even when social restrictions were in place. Across data sets, we found some support for the social participation hypothesis (i.e., the relationship between extraversion and well-being is mediated by social interactions), but the social reactivity hypothesis (i.e., extraversion moderates the relationship between social interactions and well-being) was not consistently supported. Strikingly, however, exploratory analyses showed that the social reactivity hypothesis was supported for specific facets of extraversion (i.e., sociability) and well-being (i.e., activated positive affect). Moreover, changes in social interaction patterns during the COVID-19 pandemic (e.g., decreases in face-to-face interactions and interactions with friends) were unrelated to extraversion, and more extraverted individuals did not suffer more from these changes. Taken together, these findings underline the robustness of the effect of extraversion on well-being during a societal crisis. (PsycInfo Database Record (c) 2023 APA, all rights reserved).