The HEALthy Brain and Child Development (HBCD) Study is a multi-site, prospective, longitudinal cohort study designed to examine brain, physical, biological, cognitive, behavioral, social, and emotional development from pregnancy through age 10. The study aims to understand the neurodevelopmental trajectories of children growing up in diverse environments, focusing on the short- and long-term impacts of prenatal substance use, mental health, stress, sociodemographics, biological and genetic factors, parent-child interactions, and social conditions. The HBCD Study is organized as a nationwide consortium across 27 sites, with a goal to collect multimodal data that will be made publicly available annually. The study design includes a general population cohort and a cohort with substance use exposure during pregnancy, with oversampling of individuals with specific characteristics. Data collection involves questionnaire-based surveys, neuroimaging, direct assessment of neurobehavioral performance, EEG, biospecimen collection, and wearable biosensor monitors. The study addresses limitations such as the limited number of prenatal visits and the time-consuming nature of data collection by using a jittered assessment schedule and comprehensive retention strategies. The HBCD Study is supported by the National Institutes of Health and aims to inform interventions and policies for better health and development in children.The HEALthy Brain and Child Development (HBCD) Study is a multi-site, prospective, longitudinal cohort study designed to examine brain, physical, biological, cognitive, behavioral, social, and emotional development from pregnancy through age 10. The study aims to understand the neurodevelopmental trajectories of children growing up in diverse environments, focusing on the short- and long-term impacts of prenatal substance use, mental health, stress, sociodemographics, biological and genetic factors, parent-child interactions, and social conditions. The HBCD Study is organized as a nationwide consortium across 27 sites, with a goal to collect multimodal data that will be made publicly available annually. The study design includes a general population cohort and a cohort with substance use exposure during pregnancy, with oversampling of individuals with specific characteristics. Data collection involves questionnaire-based surveys, neuroimaging, direct assessment of neurobehavioral performance, EEG, biospecimen collection, and wearable biosensor monitors. The study addresses limitations such as the limited number of prenatal visits and the time-consuming nature of data collection by using a jittered assessment schedule and comprehensive retention strategies. The HBCD Study is supported by the National Institutes of Health and aims to inform interventions and policies for better health and development in children.