The present paper reviews the theoretical and empirical literature on children and adolescents with gender variant behaviors. The organizational framework underlying this review is one that presents gender behavior in children and adolescents as a continuum rather than as a dichotomy of normal versus abnormal categories. Seven domains are reviewed in relation to gender variant behavior in general, and to Gender Identity Disorder (GID) in particular: theories of normative gender development, phenomenology, prevalence, assessment, developmental trajectories, comorbidity and treatment.