Maartje Boer

INTRODUCTION 9 1 Figure 1.1 Percentage of Adolescents Reporting Online Communication via Social Media Almost All the Time Throughout the Day Note . Data source: HBSC 2017/2018, n = 227,441 adolescents from 45 countries in Europe and Canada (Inchley et al., 2020b) and to develop their individual self (Brechwald & Prinstein, 2011; Steinberg & Morris, 2001). Social media allow adolescents to fulfil these social needs (Granic et al., 2020; Valkenburg & Peter, 2011), for example by forming and maintaining friendships by befriending peers on social network sites, direct messaging with friends through instant messengers, and receiving approval from peers through likes . Furthermore, in early and middle adolescence, it becomes highly important for adolescents to document and share their personal narratives and to learn from their peers’ personal life stories (Granic et al., 2020). The satisfaction of these needs is also facilitated by social media, because they allow adolescents to describe their lives through uploading photos or videos of themselves (and their friends) or activities on their social network site profile and to monitor their peers by browsing through photos, videos, and texts of others (Granic et al., 2020; Veissière & Stendel, 2018). In other words, social media can amplify processes that are relevant to young adolescents’ individual development. Problematic SMU Although SMU can be understood as a behavior that contributes to the development of young adolescents nowadays, concerns have been raised