The authors describe two approaches to the classification of insomnia - one was presented in earlier works, the other is currently accepted in the medical scientific community. The following three models of the etiopathogenesis of insomnia are considered: a 3-P model that identifies predisposing, precipitating, and perpetuating factors as the key ones in the development and chronicity of insomnia; a hyperarousal model that defines psychological and neurobiological hyperarousal as a factor contributing to the development of insomnia; and a sleep reactivity to stress model, according to which the pronounced premorbid sleep reactivity to stress increases the risk of developing insomnia. Hyperarousal and sleep reactivity to stress are supposed to be autonomous yet equally predisposing factors of insomnia which act reciprocally and can simultaneously contribute to the development of stress-induced insomnia. It is noteworthy that the clinical usefulness of the sleep reactivity to stress model can extend beyond the preliminary assessment of the risk of insomnia development and be used for screening patients in remission who may be at increased risk of recurrence in future and should receive supportive treatment to minimise this risk. At present, it remains unclear whether hyperarousal is the core of the disorder, its cause, risk factor, or epiphenomenon. Further investigations are required to clarify the psychological and biological basis of chronic insomnia and confirm its current theoretical and conceptual models.