Adolescent social media use and mental health problems have been on the rise, particularly following the COVID-19 pandemic. This has led to premature conclusions that social media causes adverse adolescent mental health outcomes. However, to date, there is no definitive data to support this causal link. Preliminary research has drawn associations between social media use and adolescent mental health burdens, but these data are largely cross-sectional, fail to account for potential risk and resilience factors, and do not tease apart the role of social media from offline sources associated with psychiatric disorders. In this chapter, we describe the complexities in ascertaining the direct association between social media use and adolescent mental health, particularly for marginalized youth who report greater social media use and more mental health problems. Specifically, we summarize known links between social media and adolescent mental health, describe unique aspects of this association pertaining to marginalized youth, and discuss potential adverse and protective social media factors. Importantly, we also detail the need to contextualize adolescent social media use amidst the broader youth mental health crisis, especially given the ongoing clinician shortage. Given the nascency of the field, we then provide methodological and conceptual recommendations for future research.