The formation of romantic relationships and the engagement in sexual behaviours are considered normative and salient developmental tasks for adolescents and young adults. These developmental tasks are increasingly viewed from an ecological perspective, thus not only as individual processes, but also as strongly embedded in different social contexts, including the proximal social domains of parents, peers, and partners. This special issue brings together seven recent empirical studies on adolescents' and young adults' romantic relationships and sexuality in the context of relationships and interactions with parents, peers, and partners. In this editorial introduction, we describe two important recent changes in the theoretical perspectives on emerging romantic relationships and sexual activity: from risky behaviours to normative tasks, and from individual to contextualized processes. We then discuss recent advances in empirical research on romantic relationships and sexuality of adolescents and young adults. After that, we review the seven studies in this special issue, and discuss the contributions of these studies to the existing literature. Finally, we discuss directions for future research regarding how the interrelational perspective can be further incorporated into empirical research, and how the gap between the research fields on romantic relationships and sexuality may be bridged.