More than ever, adolescents juggle with media. They use multiple media simultaneously, for example, they send text messages to their friends while watching a movie. In addition, they use media during academic and social activities, such as watching YouTube videos while doing homework. Although this rise in media multitasking among adolescents is almost inevitable, researchers have expressed concerns that media multitasking may be harmful for several aspects of adolescent development, such as attention, academic achievement, socioemotional functioning, and sleep. Despite these concerns, empirical evidence regarding potential negative consequences of media multitasking on adolescent development was limited. All chapters of this dissertation show that media multitasking and adolescent development are cross-sectionally related. However, findings on the actual impact of media multitasking on adolescent development are more nuanced. This dissertation has solely yielded small longitudinal relationships between media multitasking and some aspects of adolescent development. Although the conclusion might be that media multitasking is less problematic for adolescent development than often assumed, the findings do emphasize that there is still reason for caution regarding specific developmental domains, such as attention and sleep. Considering that media and communication devices will become increasingly integrated into adolescents’ lives, it is expected that media multitasking will continue to rise among adolescents. Therefore, the question on how adolescents should deal with the omnipresence of media and communication devices becomes even more important in the upcoming years.