Originally published in 1994 by ZERO TO THREE as the "Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood" ("DC:0-3") and revised in 2005 by ZERO TO THREE as the "Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood, Revised Edition" ("DC:0-3R"), ZERO TO THREE is now updating and revising the "DC:0-3R." This article provides background on the creation of the classification system and describes the need and process for the current revision.