The National Early Intervention Longitudinal Study (NEILS) is the first study of Part C of the Individuals With Disabilities Education Act (IDEA) early intervention system with a nationally representative sample of infants and toddlers with disabilities. This article presents national estimates of characteristics of infants and toddlers and their families at the time they entered the early intervention (EI) system. The variability in children in EI is marked by high proportions of children from low-income families, ethnic minorities, those in foster care, and males. Nearly one third (32%) are low birth weight, four times the rate in the general population. Infants and toddlers in EI are eight times more likely to be rated as having fair or poor general health. Children enter at all ages across the first 3 years of life, but those eligible because of developmental delays enter as toddlers, in comparison with those eligible because of diagnosed conditions or subject to biological or environmental risk factors, who tend to enter in the first year of life. The variability of the infants and toddlers in EI indicates that there is no typical child in EL