Sleep disturbances are common in children and adolescents but still remain unrecognized and undertreated. Several classification systems of sleep disorders are available, which include recent attempts to develop more specific nosologic categories that reflect developmental aspects of sleep. The prevalence of sleep disorders has been studied across various samples of healthy, typically developing children and those with special medical, psychiatric, and neurodevelopmental needs. Sleep disorders are highly prevalent in children and adolescents with psychiatric disorders, making it important for mental health professionals to be aware of sleep problems and to address them in the context of psychiatric comorbidities.