Social media platforms have established themselves as one of the primary ways adolescents interact with and observe their peers. Several features of social media (e.g., availability, asynchronicity, permanence) may transform the way that adolescents interact with their peers. This chapter reviews the features of social media that may shape peer relationships on these platforms, focusing on three important aspects of peer relationships in adolescents: peer influence, social connection versus isolation, and popularity/status). Peer influence is likely amplified in social media, as adolescents are able to view (and be viewed by) their entire peer network at any time. The impact this has on adolescents’ perceptions and use of substances is discussed. Although social media are inherently relationship oriented, there has been debate on whether these platforms facilitate or undermine meaningful connection with peers. The differential role of active versus passive use is discussed. Finally, this chapter examines how social media promote an emphasis on popularity and presenting a curated self-image. The chapter will conclude with a discussion of the challenges and opportunities that social media presents for researchers, and future directions for researchers to understand how these media impact adolescents’ peer relationships.