This article describes how the "developmental structuralist" theory of emotional development has evolved over 25 years into the developmental-individual difference-relationship (DIR[R]) approach to assessment and intervention. ZERO TO THREE and the Interdisciplinary Council for Developmental and Learning Disorders (ICDL) trace their roots to the Clinical Infant Development Program of the National Institute of Mental Health. In the Developmental, Individual-Difference, Relationship-Based (DIR[R]) model, "D" stands for functional, emotional developmental capacities; "I" refers to individual differences, and "R" describes the child's relationships with caregivers and culture. The DIR model of intervention (sometimes referred to as Floortime[TM]) includes direct work with the child, work with parents and caregivers, and work with caregiver and family patterns.