Prior research indicates that Facebook usage predicts declines in subjective well-being over time.How does this come about?We examined this issue in 2 studies using experimental and field methods.In Study 1, cueing people in the laboratory to use Facebook passively (rather than actively) led to declines in affective well-being over time.Study 2 replicated these findings in the field using experience-sampling techniques.It also demonstrated how passive Facebook usage leads to declines in affective well-being: by increasing envy.Critically, the relationship between passive Facebook usage and changes in affective well-being remained significant when controlling for active Facebook use, non-Facebook online social network usage, and direct social interactions, highlighting the specificity of this result.These findings demonstrate that passive Facebook usage undermines affective well-being.