The HEALTHy Brain and Child Development (HBCD) Study is a multi-site, longitudinal cohort study aiming to examine brain, physical, biological, cognitive, behavioral, social, and emotional development starting in pregnancy and continuing through age 10. The study seeks to understand the short- and long-term impacts of various harmful and protective factors, including prenatal substance use, on developmental trajectories. The HBCD Study is organized as a nationwide consortium across 27 sites and will collect multimodal data that will be made publicly available on a yearly basis. The study design includes a general population cohort and a substance use (SU) cohort, with participants recruited based on specific criteria. The study involves a comprehensive data collection process, including assessments, neuroimaging, biospecimens, and environmental exposures. The HBCD Study also emphasizes diversity, equity, and inclusion, with a focus on ensuring that all participants are adequately compensated and that the study is conducted with ethical standards. The study is supported by the National Institutes of Health (NIH) and other federal partners, and it aims to inform future interventions and policies to promote wellbeing and resilience in all children. The study involves a complex data management system, with data collected through multiple visits and assessments, and data use is regulated through an application and approval process. The HBCD Study is designed to address major knowledge gaps in developmental trajectories from infancy through the pre-adolescent period, and it aims to provide a comprehensive understanding of the neurodevelopmental processes that occur during early childhood. The study also includes a focus on participant retention, with strategies to ensure continued participation and engagement. The HBCD Study is a significant contribution to the field of developmental neuroscience, providing a unique opportunity to study the effects of various environmental factors on brain and child development.The HEALTHy Brain and Child Development (HBCD) Study is a multi-site, longitudinal cohort study aiming to examine brain, physical, biological, cognitive, behavioral, social, and emotional development starting in pregnancy and continuing through age 10. The study seeks to understand the short- and long-term impacts of various harmful and protective factors, including prenatal substance use, on developmental trajectories. The HBCD Study is organized as a nationwide consortium across 27 sites and will collect multimodal data that will be made publicly available on a yearly basis. The study design includes a general population cohort and a substance use (SU) cohort, with participants recruited based on specific criteria. The study involves a comprehensive data collection process, including assessments, neuroimaging, biospecimens, and environmental exposures. The HBCD Study also emphasizes diversity, equity, and inclusion, with a focus on ensuring that all participants are adequately compensated and that the study is conducted with ethical standards. The study is supported by the National Institutes of Health (NIH) and other federal partners, and it aims to inform future interventions and policies to promote wellbeing and resilience in all children. The study involves a complex data management system, with data collected through multiple visits and assessments, and data use is regulated through an application and approval process. The HBCD Study is designed to address major knowledge gaps in developmental trajectories from infancy through the pre-adolescent period, and it aims to provide a comprehensive understanding of the neurodevelopmental processes that occur during early childhood. The study also includes a focus on participant retention, with strategies to ensure continued participation and engagement. The HBCD Study is a significant contribution to the field of developmental neuroscience, providing a unique opportunity to study the effects of various environmental factors on brain and child development.