Insomnia is one of the most common health issues, with occasional symptoms affecting up to 50% of the general population. Lack of sleep is associated with many negative health effects. A new evolutionary hypothesis has been proposed to explain the mechanism behind insomnia symptoms. The evolutionary-emotional hypothesis proposes that while acute insomnia might be advantageous from an evolutionary perspective, chronic insomnia is maladaptive and may follow from a failure or delay of fear extinction. The aim of the current thesis was to investigate which neural mechanisms might be at work if one is to consider the evolutionaryemotional hypothesis about the causes of insomnia plausible and to review studies from cognitive neuroscience to discover what support there might be for the hypothesis. Studies have found heightened activation in fear-related brain areas in insomnia patients. Delayed fear extinction and altered emotion regulation circuitry, among other things, were also observed for insomnia patients. However, few experimental studies on the effect of fear extinction on sleep in insomnia patients have been conducted. At this time, some emerging evidence lends support for the evolutionary-emotional hypothesis of insomnia, but more studies that directly assess fear conditioning and fear extinction processes in insomnia patients are needed to assess the explanatory power of the theory.