“This study is part of the NIH’s Helping to End Addiction Long-term (HEAL) initiative to speed scientific solutions to the national opioid public health crisis. The NIH HEAL Initiative bolsters research across NIH to improve treatment for opioid misuse and addiction.” The HEALthy Brain and Child Development study (HBCD) under the leadership and management of the HBCD Administrative Core (HCAC) will deploy a harmonized, optimized, and innovative set of neuroimaging measures complemented by an extensive battery of behavioral, physiological, and psychological tools, and biospecimens to understand neurodevelopmental trajectories in a sample of 7,500 mothers and infants enrolled at sites across the US. To address these broad objectives, the HCAC will oversee study design, development of the common protocol, monitoring for recruitment and retention, monitoring for site performance, provision for training, ethical policies, management of study communications, and oversight of processes for considering study modifications. These activities will support the objective of HBCD to release a high-quality research dataset on an annual basis. In the first year of study preparations for the launch of HBCD, several modifications and clarifications to the common core protocol have been recommended and adopted by the HBCD Steering Committee. This has led to the need to ensure that common and rigorous training, administration, and validation protocols be developed and implemented for three key study measures: the Bayley Scales of Infant Development-4 (BSID-4), the ERICA parent-child interaction measure, and the Preschool Age Psychiatric Assessment (PAPA), all of which will be administered during the first five-year cycle for the HBCD study. With this Supplement, the HCAC will be responsible for centralized training and monitoring for fidelity of site administration of the BSID-4, will oversee centralized training for site administration and centralized coding of the ERICA assessments, and will oversee centralized training and administration of the PAPA measure. These additional HCAC efforts will help to limit bias in these key assessments and are consistent with the role of the HCAC in protocol training and monitoring for performance.