Consciousness is the most general ability to subjective experience, because everything we know, we know from experiencing it. Its main components are wakefulness, qualitative experiences (e.g. to feel, see, or taste), and intentional states. Disorders of Consciousness (DoC) are conditions in which one, two, or all three components of consciousness described above, are disturbed. One central question is, whether the three components of consciousness are dissociable. Another issue is how modern neurophysiological techniques can reveal covert conscious functions in patients with extremely severe DoC.