Romantic relationship formation and the engagement in sexual behaviors are normative and salient developmental tasks for adolescents and young adults. These developmental tasks are increasingly viewed from an ecological perspective, thus as strongly embedded in different social contexts, including the proximal social domains of parents, peers, and partners. This volume brings together seven recent empirical studies on adolescents’ and young adults’ romantic relationships and sexuality in the context of relationships 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 behaviors 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 volume, and discuss the contributions of these studies to the existing literature. Finally, we discuss directions for future research regarding how to further incorporate the interrelational perspective in empirical research on these topics, and how to bridge the gap between the research fields on romantic relationships and sexuality. This book was originally published as a special issue of the European Journal of Developmental Psychology.