Insomnia is most often thought of as both a medical sign and a symptom that can accompany several sleep, medical, and psychiatric disorders characterized by a persistent difficulty falling asleep and/or staying asleep or sleep of poor quality.

Insomnia is typically followed by functional impairment while awake. Insomnia can occur at any age, but it is particularly common in the elderly. Insomnia can be grouped into primary and secondary insomnia. Cognitive behavioral therapy is useful in insomnia that is present for a long duration.