This commentary discusses the decisions of child protective service (CPS) investigators to substantiate mothers for failure-to-protect (FTP) in child sexual abuse cases. Four areas are identified in which the scientific literature remains inadequate to fully inform child maltreatment researchers, CPS practitioners and child welfare policymakers on models and outcomes for FTP substantiation decisions. Attention is called to the need for more information about how differences in statutory definitions, common guidelines, and professional education and training influence FTP substantiation decisions. Current gaps in the knowledge base on FTP and nonoffending caregivers are highlighted.