Insomnia affects 10% to 30% of the population with a total cost of $92.5 to $107.5 billion annually. Short-term, chronic, and other types of insomnia are the three major categories according to the International Classification of Sleep Disorders, 3rd ed. The criteria for diagnosis are difficulty falling asleep, difficulty staying asleep, or early awakening despite the opportunity for sleep; symptoms must be associated with impaired daytime functioning and occur at least three times per week for at least one month. Factors associated with the onset of insomnia include a personal or family history of insomnia, easy arousability, poor self-reported health, and chronic pain. Insomnia is more common in women, especially following menopause and during late pregnancy, and in older adults. A comprehensive sleep history can confirm the diagnosis. Psychiatric and medical problems, medication use, and substance abuse should be ruled out as contributing factors. Treatment of comorbid conditions alone may not resolve insomnia. Patients with movement disorders (e.g., restless legs syndrome, periodic limb movement disorder), circadian rhythm disorders, or breathing disorders (e.g., obstructive sleep apnea) must be identified and treated appropriately. Chronic insomnia is associated with cognitive difficulties, anxiety and depression, poor work performance, decreased quality of life, and increased risk of cardiovascular disease and all-cause mortality. Insomnia can be treated with nonpharmacologic and pharmacologic therapies. Nonpharmacologic therapies include sleep hygiene, cognitive behavior therapy, relaxation therapy, multicomponent therapy, and paradoxical intention. Referral to a sleep specialist may be considered for refractory cases. Copyright (C) 2015 American Academy of Family Physicians.)