This report describes the psychometric characteristics and related methodology of the 9-month data collection of the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B), which is sponsored by the U.S. Department of Education, National Center for Education Statistics (NCES) in the Institute of Education Sciences, in collaboration with several health, education, and human services agencies. In the base year collection of the ECLS-B, when the children were about 9 months of age, the study interviewed parents (typically the biological mother), assessed children, and gathered information directly from the children's father figure. This report describes the psychometric instruments of the direct child assessments, including the Bayley Short Form-Research Edition (BSF-R), the Nursing Child Assessment Teaching Scale (NCATS), the physical measurements, and interviewer-completed observations of children's behavior. The report also describes some indirect assessments in the parent interview.