Book excerpt: This issue of Sleep Medicine Clinics focuses on Medications and their Effects on Sleep and Wake, with topics including: Sleep-wake neurochemistry; Effect of sleep and circadian rhythm on pharmacokinetics and pharmacodynamics; Drugs used in insomnia and non restorative sleep; Drug-induced exessive sleepiness; Drug-induced insomnia; Drug-induced sleep disordered breathing and ventilatory impairment; Drug-induced parasomnias and movement disorders; Abuse and dependency on sleep and waking; Sleep-related drug therapy in special conditions: children; Sleep-related drug therapy in special conditions: pregnancy; Sleep-related drug therapy in special conditions: the elderly; Medicolegal and social consequences of sleep disorders; and Tapering sleep-related drug therapy.