To better understand the development of mental health problems, it is of fundamental importance to focus on both adolescence – as this is the age period where most psychopathology develops – and social processes – as psychological distress is largely interpersonal in nature. In addition, certain parenting styles are strong predictors of both social and mental health outcomes. However, relatively little is known about how these different factors interrelate in adolescent day-to-day life. Within this dissertation, we draw on data collected with the Experience Sampling Method to gain a greater, more ecologically valid insight into the relationship between parenting, social processes, and psychopathology in adolescents.In Chapter 3, we present the case for why assessments of social processes require a greater consideration of ecological validity – and of daily life. Social cognition assessments in psychosis are discussed, but the arguments posited here are relevant for all types of social assessments in mental health research.In Chapters 4 to 6, the interrelationships between parenting, psychopathology, and daily-life social interactions are studied in three empirical studies using two large adolescent experience sampling data sets. In Chapter 4, we find how parental care and control are largely related to the experienced quality of daily-life social interactions rather than to its quantity. A similar finding is reported in Chapter 5, where we see consistent associations between the quality of daily-life social interactions and mean psychopathology level – and less consistent relationships between the quantity of social interactions and psychopathology. Finally, in Chapter 6, these relationships are investigated in one comprehensive model, including more specific parenting styles, and daily social interactions in different companies. In this model, paternal autonomy support and an altered quality of daily social interactions have unique associations with psychopathology levels. Taken together, these findings indicate a particular relevance of the quality of day-to-day social interactions for better understanding psychopathological development. As the social lives of contemporary adolescents are happening largely online as well as offline, in Chapter 7, we assess how adolescents experience online vs. face-to-face social interactions at the moment that they engage in them. We find how participants report more affective benefits when engaging in face-to-face interactions compared to online interactions, and, in contrast to our hypotheses, we report no moderating effects of social resources on the strength of these benefits. The investigation of adolescents` social lives and their relation with mental health became much more relevant as COVID-19 hit, when restrictions prevented people from interacting with each other. In the last study, presented in Chapter 8, we investigate differences in young people’s mental health and day-to-day social interactions, from before the pandemic to early in the pandemic (May 2020). We find how face-to-face interactions decreased and online interactions increased, but more surprisingly, that general psychopathology levels were lower than expected and that anxiety levels had even decreased. Moreover, the relationship between the quality of social interactions and psychopathology had become stronger during the pandemic, indicating the relevance of high-quality social interaction during times of social deprivation. In sum, in this thesis, I target the uniquely relevant momentary social interaction to better understand the social development of young people – and to assess when this might go awry. Across all studies, the quality of social interactions seems fundamentally important. Cross-level relationships seem to exist between general parenting perceptions and how social interactions are experienced in the moment, and between those daily-life social experiences and psychopathology levels. Future research should further disentangle these processes longitudinally to gain greater insight into the temporal ordering of these relationships. Finally, for the development of momentary interventions aimed at relieving social distress, a focus on the quality rather than the quantity of social behaviors is likely most helpful.