The overall aim of this thesis is to examine different aspects of Swedish adolescents’ everyday environment in a digital world. Drawing on ecological and psychosocial developmental theories I will discuss social, sexual, and biological aspects of the Internet as an everyday environment, an environment in which most adolescents spend a great deal of time. The thesis comprises four studies, all examining different aspects of the developmental stage of adolescence. Study I focused primarily on the extent to which adolescents encounter explicit online content, such as pornographic, violent, and/or hateful material, and how they react to it. What feelings are associated with explicit online content? And how do adolescents deal with those feelings? In study I we analyzed questionnaire data collected from 226 adolescents between the ages of 13 and 15 (47% girls and 53% boys). In line with other studies on the subject, the results showed that many Swedish adolescents are exposed either intentionally or unintentionally to explicit online content. Adolescents in this study showed surprisingly low emotional response to their exposure to explicit content. Their coping strategies center on personal agency, with most choosing to avoid or block unwelcome content rather than turn to parents or siblings for support and advice. Almost no significant gender differences were found in the choice of coping strategies, except that young men were more likely to avoid a site than were young women. Study II focused on the association between various parental and child factors and the parents’ attitudes toward adolescents’ online sexual activities. The study was based on questionnaire data collected from parents (78% mothers) and adolescents (54% girls) in 496 families. Results showed that parental attitudes toward adolescents’ offline and online sexual activities are closely related, although parents are more permissive in the offline setting. Parents’ attitudes toward online sexuality are not only correlated with their attitudes toward sexuality in traditional settings, but also by their preferences on the Internet. Parental attitudes were found to differ by the sex of the parent and the sex and age of the child. The link between fathers’ attitudes and adolescents’ online sexual activities was mediated by parental rules, suggesting that communication is part of the transmission of values. The focus of study III was on the link between adolescent boys’ pubertal timing and their offline and online romantic and sexual activities. The study was based on questionnaire data obtained from 142 early adolescent Swedish boys. Participants reported on stagenormative (physical) and peer-normative aspects of pubertal timing, and on offline and online romantic and sexual activities. Both aspects of pubertal timing were related to romantic and sexual activity offline, but only the stage-normative measure was linked to sexual activities online. In study IV the focus was on the relationship between sexual and romantic activity in a traditional offline context and similar activities online. Longitudinal questionnaire data were obtained from 440 adolescents over three years. Results revealed that both offline and online sexual activity increased over time within the group. We found that results for girls showed a somewhat larger effect, indicating that the link between offline and online sexual activity is largest within the female group. Results also revealed a small but significant increase in the slope for participation in offline sexual activity with online sexual activity as a predictor – but only for boys – indicating that the link between online and offline sexual activity (i.e., the other way around) only exists within the male group. Thus, as boys’ participation in sexual activity increases online, so it also does offline. The article concludes that adolescents’ romantic and sexual activities online are tied to their physical, offline equivalent and so the Internet can be regarded as an important context for sexual development. Taken together, the individual studies suggest that The Internet, as an everyday environment is linked to several aspects of the developmental phase of adolescence. Further studies should continue to explore the effect of the Internet on adolescents’ developmental tasks.