In this article, we provide definitional clarity for the construct of social withdrawal as it was originally construed, and review the original theoretical and conceptual bases that led to the first research program dedicated to the developmental study of social withdrawal (the Waterloo Longitudinal Project). We also describe correlates (e.g., social and social-cognitive incompetence), precursors (e.g., dispositional characteristics, parenting, insecure attachment), and consequences (e.g., peer rejection and victimization, negative self-regard, anxiety) of social withdrawal, and discuss how the study of this type of withdrawal led to a novel intervention that targets risk factors that predict social withdrawal and its negative consequences.