Insomnia is a common complaint that can present independently or comorbidly with another medical disorder (e.g. pain) or psychiatric disorder (e.g. depression). Insomnia is the most prevalent sleep disorder and affects large proportions of the population on a situational, recurrent, or persistent basis. It carries a heavy burden for both patients and the healthcare system as evidenced by its effect on quality of life, and on psychological, occupational, and economic domains. Insomnia is often unrecognized and untreated because of barriers to assessment and management. Insomnia is characterized by subjective complaints about dissatisfaction with sleep quality or duration, difficulty in night or too early in the morning or non-restorative or falling asleep at bedtime, waking up in the middle of the poor quality sleep. This chapter covers the epidemiology of chronic insomnia, pathophysiological mechanisms, assessment and diagnosis, cognitive behavioral therapy, practical considerations for CBT implementation, pharmacotherapy, and combined CBT and drug treatment.