Diagnosis of infants and young children has evolved rapidly. The  DC: 0-3R™ is a framework of developmentally informed, descriptive categories within a multi-axial system. This Workshop addresses clinicians and supervisors, reviewing the organizing principles of the Diagnostic Classification: 0-3R™. It details a brief history of the development of the system and discusses the evolving use of the diagnostic system for research, reimbursement, and clinical practice.  An overview of this multi-axial system is presented.  Axis I disorders are reviewed highlighting those unique to young children. Regulatory disorders, which describe children with constitutional physiological, sensory, motor, or affective processing difficulties and difficulties in regulating behavior, provide a new approach to understanding young children. Axis II, Relationship Classification, and the Parent-Infant Relationship Global Assessment Scale, focuses on patterns of relating and disorders specific to a relationship. Axis V, which describes assessment of the child’s functional capabilities within different relationships, is presented with hands-on practice. The Workshop provides videotaped case presentations, with an emphasis on diagnostic decision-making and case formulation.