The first years of life have a profound impact on later behavioural, emotional and social development. An intriguing and modifiable risk factor for later psychopathology is the early regulation of bodily functions, such as the sleep-wake cycle, self-soothing and food ingestion, which goes awry in about 20% of infants leading to regulatory problems (RPs) with crying, sleeping and/or feeding. About 2-8% of infants and toddlers experience multiple or prolonged RPs. Mounting evidence shows that RPs can have adverse long-term effects on behavioural, emotional and/or social outcomes. The proposed project will investigate the impact of early RPs on mental health outcomes from childhood to adulthood, examining multimodal neurobiological markers as possible underlying mechanisms. We will go beyond the state of-the-art in three ways. Firstly, we will analyse rich phenotypic and neuroimaging data of three population-based studies from three countries (Generation R, ALSPAC and BLS). To enable cross-timepoint and cross-dataset brain surface analysis, we will develop novel robust vertex-wise mixed modelling, meta-analysis and federated mega-analysis tools as part of an existing open-source R package. Secondly, we will examine neurobiological pathways of the RP-mental health association, via brain structure (i.e., cortex morphology) and function (i.e., intrinsic functional connectivity). Thirdly, we will employ the hierarchical dimensional HiTOP framework to characterize adverse outcomes of early RPs with better precision and generalizability. This may result in new findings on neurobiology and effects of RPs on dimensional mental health phenotypes, and crosswalk models for the research community.