Insomnia is one of the most frequently encountered disorders in general clinical practices. At present, the most commonly used therapy for insomnia is pharmacotherapy. There are some problems in pharmacotherapy such as side effects. Therefore nonpharmacological therapy for insomnia is needed. The cognitive behavior therapy for insomnia (CBT-I) is a nonpharmacological therapy attracting attention most. CBT-I not only alleviates insomnia symptoms in patients but also enables them to reduce/discontinue the use of hypnotics. I reviewed a study about the effectiveness of CBT-I and commented the future directions of CBT-I.