Insomnia is the most common sleep disorder worldwide, characterized by persistent difficulty initiating sleep (falling asleep), maintaining sleep (staying asleep), or waking earlier than desired, combined with daytime consequences such as fatigue, impaired concentration, mood disturbance, or reduced performance. By definition, insomnia occurs despite having adequate opportunity and circumstances for sleep, distinguishing it from sleep deprivation due to external circumstances. Insomnia is classified as acute or chronic. Acute insomnia, also called short-term or adjustment insomnia, typically lasts a few days to a few weeks and is usually triggered by an identifiable stressor such as illness, a major life event, or travel. Chronic insomnia is defined as difficulty sleeping at least three nights per week for three months or more, and may persist for years without appropriate treatment. The causes of insomnia are varied and often interrelated. Psychological factors — particularly stress, anxiety, and depression — are among the most significant contributors. Negative thoughts and behaviors associated with sleep (such as spending excessive time in bed while awake, worrying about sleep, and engaging in stimulating activities before bed) can perpetuate and worsen insomnia over time. Cognitive behavioral therapy for insomnia (CBT-I) is the most effective and recommended first-line treatment for chronic insomnia. CBT-I addresses the underlying cognitive and behavioral factors maintaining insomnia and has been shown to produce lasting improvements. Sleep medications may be used for short-term relief but are generally not recommended as a long-term solution due to the risk of dependency and side effects. Understanding and addressing the root causes of insomnia, alongside good sleep hygiene practices, is central to effective management.