Worry is a common phenomenon in children and adolescents, with some experiencing excessive worries that cause significant distress and interference. The metacognitive model of generalized anxiety disorder (Wells 1995, 2009) was developed to explain cognitive processes associated with pathological worry in adults, particularly the role of positive and negative beliefs about worry. This review evaluates the application of the model in understanding child and adolescent worry. Other key issues reviewed include the link between cognitive and metacognitive development and worry, and the measurement of worry and metacognitive worry in young people. Implications of these findings and directions for future research are discussed.