Evidence increasingly suggests that cognitive impairment is common in intensive care unit survivors, although the nature, severity, and natural history remain unclear. Although the cognitive impairments improve over time in some individuals, they often fail to completely abate. While the functional correlates of these impairments are under-studied, cognitive impairments may adversely impact quality of life, ability to return to work or to work at previously established levels, and ability to function effectively in emotional and interpersonal domains. The potential etiologies of cognitive impairments in intensive care unit survivors are not fully understood and are likely heterogeneous and vary widely across patients. The contributions of these many factors may be particularly significant in patients with pre-existing vulnerabilities for the development of cognitive impairments, such as mild cognitive impairment, dementia, prior traumatic brain injury, or other comorbid disorders, as well as predisposing genetic factors.