This special issue includes empirical research on the relationship between sleep and cognition, focusing on a variety of populations: Young, middle-aged, and older adults with insomnia, and patients with chronic pain. The editors of this special issue note the overlap between the dysfunctional cognitions observed in people with sleep problems with the cognitions observed in a variety of psychological and medial disorders. The editors call for researchers to integrate sleep into our models of cognitive dysfunction, medical and psychological pathology and well being, paying particular attention to how sleep disturbances may maintain or exacerbate said pathologies.