Maartje Boer

CHAPTER 1 8 Introduction Social media have become increasingly popular in the past decades (Anderson & Smith, 2021), especially among early and middle adolescents (Anderson & Jiang, 2018; Lenhart et al., 2015). Social media are social network sites, such as Instagram and Facebook, and instant messengers, including SnapChat and Whatsapp. Social network sites allow users to create and maintain a personal profile with photos, videos, and texts to share with an online social network. Instant messengers facilitate sending personalized direct messages to others through private chat functions. Many adolescents use social media through internet applications on their smartphones (Eurostat, 2015), which allows them to access social media any time at any place. Research among 13- to 17-year-olds U.S. adolescents showed that the percentage of adolescents reporting being almost online constantly has almost doubled within three years: from 24% in 2015, to 45% in 2018 (Anderson & Jiang, 2018; Lenhart et al., 2015). Findings from research among European and Canadian adolescents indicated that in 2017 and 2018, 41% of all 15-year- olds interacted with friends and others through social media almost all the time throughout the day (Inchley et al., 2020b). In other research among European adolescents collected between 2017 and 2019 it was found that 81% of the 15- and 16-year-olds reported using a smartphone to access internet several times or almost all the time throughout the day. Among this group, the average time spent online was almost four hours a day and 77% reported visiting social network sites at least once a day (Smahel et al., 2020). These studies illustrate that, nowadays, many adolescents have integrated social media use (SMU) into their daily lives. Furthermore, social media are popular across both genders and during both early and middle adolescence (Inchley et al., 2020b; Smahel et al., 2020), although research showed that girls use social media more frequently than boys and the popularity of social media increases with age (Figure 1.1; Inchley et al., 2020b). From a developmental point of view, it is understandable why social media are so popular among young adolescents. During early adolescence, making close friends, belonging to peer groups, and being accepted by peers becomes increasingly important. More specifically, peers offer young adolescents opportunities to experiment with and discover new behaviors, morals, and beliefs and as such, to become more autonomous from parents