Many individuals who sustain severe brain injury experience prolonged or permanent disorders of consciousness. While these disorders may appear homogeneous, important distinctions exist in prognosis and clinical management. Studies suggest, however, that the incidence of diagnostic inaccuracy is high in both acute care and rehabilitation settings. In this paper, we review consensus-based diagnostic and prognostic criteria for the vegetative and minimally conscious states. We also discuss recent developments and future directions for research in this area.