Delirium, stupor and coma are common clinical states that confront clinicians in almost every medical specialty. With appropriate diagnosis and treatment, coma can often be treated successfully. Conversely, delay in diagnosis and treatment may be lethal. This monograph provides an update on the clinical approach that was laid out in the previous 3 editions. It describes an approach for the physician at the bedside to diagnose and treat alterations of consciousness, based on pathophysiologic principles. The book begins with a description of the physiology of consciousness and the pathophysiology of disorders of consciousness. It continues with a description of the approach to a patient with a disorder of consciousness, emphasizing the bedside examination, but including the use of modern imaging techniques. The important structural and metabolic causes of coma are reviewed in detail. It then describes the emergency treatment, both medical and surgical, of patients with specific disorders of consciousness and their prognosis. New chapters describe the approach to the diagnosis of brain death and the clinical physiology of the vegetative state and minimally conscious state, as well as the ethics of dealing with such patients and their families. The book is aimed at medical students and residents, in fields from internal medicine and pediatrics to emergency medicine, surgery, neurology, neurosurgery, and psychiatry, who are likely to encounter patients with disordered states of consciousness. It includes historical background and basic neurophysiology that is important for those in the clinical neurosciences, but also lays out a practical approach to the comatose patient that is an important part of the repertoire of all clinicians who provide emergency care for patients with disorders of consciousness.