Approximately 35% of the general population suffer from insomnia symptoms, whereas roughly 10% meet the criteria for insomnia disorder (Ohayon, 2002; Ohayon & Reynolds, 2009). Insomnia increases the risk of developing other mental disorders and somatic morbidities and is associated with high costs for health-care systems (Riemann et al., 2015). Despite the socioeconomic and health impact of insomnia, its pathophysiology has not been fully identified. In order to better understand the underlying neurobiology, an increasing number of studies use functional imaging techniques to investigate the neural correlates and mechanisms that may contribute to the development and maintenance of the disease (Spiegelhalder et al., 2015). Several studies have used resting state fMRI functional connectivity, a method that allows the analysis of temporal correlations between spatially distinct brain regions, and that gives insight about the association between insomnia symptoms and alterations in the brain’s inherent organization and functioning. Functional connectivity research in insomnia has mainly focused on the default mode network (DMN), a large-scale brain network involved in worry and rumination, which are common symptoms of insomnia (Schiel et al., 2020). However, there are inconsistent findings, with studies reporting increased FC (Leerssen et al., 2019), unaltered FC (Regen et al., 2016), and reduced FC (Nie et al., 2015) between nodes of the DMN in insomnia patients compared to healthy good sleepers. Furthermore, a number of studies have examined FC within the salience network (SN), which promotes salience detection and emotion processing, and is thought to integrate physiological arousal with conscious appraisal (Uddin, 2015). Dysfunctional connectivity within the SN may help explain deficits in affective and cognitive control processing in insomnia, such as increased experiences of negative emotions (Baglioni et al., 2010) and an attentional bias for sleep-related stimuli (MacMahon et al., 2006). Supporting this idea, Chen et al. (2014) found greater involvement of the anterior insula with salience networks in people with insomnia, whereas Huang et al. (2012) reported decreased functional connectivity mainly between the amygdala and insula. Regarding the SN’s role in mediating the dynamic switching between recruitment of other functional brain networks (Sridharan et al., 2008), reduced FC variability between the anterior SN and the left executive-control network has been found in people with insomnia and may underlie deficient cognitive-affective flexibility (Wei et al., 2020). Although recent research expands the knowledge on atypical connectivity patterns associated with insomnia, inconsistencies remain, which may be attributed to heterogonous sampling, methodological differences, and/or small sample sizes (Tahmasian et al., 2018). Moreover, it is possible that insomnia is characterized by minor and widely distributed FC alterations (Van Someren, 2020). However, whole-brain FC analyses with sufficient power to detect such small effects would require large sample sizes. Considering these notions, the proposed project plans to investigate the association between whole-brain resting state functional connectivity and insomnia symptoms in a large population-based sample.