Approximately 25% of all children experience some type of sleep problem at some point during childhood. A number of studies have examined the prevalence of parent- and child-reported sleep complaints in large samples of healthy, typically developing children and adolescents; many of these have also further delineated the association between disrupted sleep and behavioral concerns. Sleep problems are even more prevalent in children and adolescents with chronic medical, neurodevelopmental, and psychiatric conditions. It is important to note that definitions of normal sleep patterns, sleep requirements, and sleep disorders in childhood must necessarily incorporate the wide range of normal developmental and physical maturational changes across childhood and adolescence, and cultural, environmental, and social influences.