Sleep is a physiological process of homeostasis, which has been incorporated into the dual process mode of sleep regulation, namely sleep homeostasis and circadian rhythm regulation. If there is a functional disorder of the above two types of regulation or the wake-up system is overfunctioning, insomnia may occur. Insomnia has a tendency of becoming chronic. According to the 3P model, acute insomnia occurs when individual susceptibility and innate tendency are challenged by predisposing factors. While negative thoughts and non-adaptive coping behaviors will produce conditional arousal, which is learned and maintained to form chronic insomnia after repetitions. There is a lack of effective treatments for chronic insomnia. The cognitive behavioral therapy for insomnia (CBT-I) is a non-drug therapy which has an effect equivalent to hypnotics without side effects, and it produces less frequent recurrence and a long-term effect superior to hypnotics. This treatment includes progressive relaxation, biofeedback, cognitive methods, stimulus control, time therapy, and sleep restriction therapy. However, this treatment has not been fully utilized in clinical practice. CBT-I is recommended to be used as a first-line treatment.