Book excerpt: This issue describes in detail the most current thinking on the way genes affect and determine sleep patterns, behaviors, disorders and needs. Sleep researchers continue to study genetic markers that may someday lead to a personalized approach to treatment of sleep disorders. The genetics of restless legs syndrome, narcolepsy, circadian rhythm disorders, obstructive sleep apnea, parasomnias, and insomnia are discussed. A solid understanding of the role genetics and molecular biology play in sleep will aid clinicians in diagnosing and treating these disorders, as well as advising their patients.