To date, most explanations of adult social development within the field of psychology assume universal age-related processes. The majority of these explanations, however, stem from studies on a limited number of cohorts that were socialized in specific social contexts. As a consequence, the current knowledge on adult social development confounds age-related and contextual influences. We argue that it is essential to disentangle these influences to better understand adult social development. In this article, we apply the theoretical framework of developmental contextualism and provide explanations for adult social development that are firmly based on the sociohistorical context that a cohort experienced during young adulthood. This hypothesis is discussed with the example of romantic relationships. We argue that the relatively strong value that today's older adults ascribe to close social ties might be rooted in experiences of limited life-path options, existential concerns, and stressful historical events (i.e., Great Depression, World War II, postwar era) during their young-adult years. Today's young adults, conversely, are socialized in rapidly changing social structures with increasing diversity in life-path options and in relative security with regard to basic material and security needs. We explore how these experiences might shape the future social development of today's young adults with respect to relationship contexts (e.g., living arrangements, digitalization) and relationship needs (e.g., exploration, self-actualization). We conclude with theoretical and methodological recommendations for future research that will be amply equipped to systematically investigate both age-related and contextual influences that drive development in any previous, present, and forthcoming cohort. (PsycInfo Database Record (c) 2020 APA, all rights reserved).