The number of sleep problems among adolescents is alarmingly high and even seems to have intensified over the past decades. Excessive social media use is often blamed for this. Yet, the (little) empirical research to support this claim is characterized by conceptual and methodological shortcomings. Departing from a theory-driven and person-specific approach, the overall aim of this project is to advance the emerging literature on adolescents’ social media use and sleep by gaining deeper insights in the motivational dynamics underlying adolescents’ social media use. First, harmonious, and obsessive social media use will be distinguished as two qualitatively different motivational regulations of social media use, which are expected to yield a different impact on adolescents’ sleep. Second, we aim to target underlying roots of adolescents’ social media use, which are expected to be valuable even when changes in the social media landscape occur (such as in platforms, content, and features). Third, methodologically, we will rely on intensive repeated measures design that allows for an estimation of heterogeneity in adolescents’ individual susceptibility to social media use in terms of sleep. Lastly, by developing and testing a need-crafting intervention, we aim to help adolescents to better regulate their social media use, to maximize the benefits of its, while limiting the consequences for poor sleep.