Book excerpt: While both positive and negative peer interactions have long been a focus of scientific interest, much less attention has been given to children who tend to refrain from interacting with peers. This volume brings together leading authorities to review progress in understanding the development, causes, and consequences of shyness and social withdrawal. Compelling topics include: *The interplay of biological, psychological, family, and interpersonal processes in shyness and social withdrawal from infancy through adolescence. *The impact on peer relationships and academic performance. *Links among shyness, social withdrawal, and social anxiety disorder. *The positive side of unsociability—when to "leave children alone." *Implications for clinical practice and educational interventions.