This text is an update of a classic work on diagnosing the cause of coma, with the addition of new sections on the treatment of comatose patients. The first chapter provides an up-to-date review on the brain mechanisms that maintain a conscious state in humans and how lesions that damage these mechanisms cause loss of consciousness or coma. The second chapter reviews the neurological examination of the comatose patient, which provides the basis for determining whether the patient is suffering from a structural brain injury causing the coma or from a metabolic disorder of consciousness. The third and fourth chapters review the pathophysiology of structural lesions causing coma and the specific disease states that result in coma. Chapter 5 is a comprehensive treatment of the many causes of metabolic coma. Chapter 6 review psychiatric causes of unresponsiveness and how to identify and treat them. Chapters 7 and 8 review the overall emergency treatment of comatose patients, followed by the treatment of specific causes of coma. Chapter 9 examines the long-term outcomes of coma, including the minimally conscious state and the persistent vegetative state, how they can be distinguished, and their implications for eventual useful recovery. Chapter 10 reviews the topic of brain death, the standards for examination of a patient that are required to make the determination of brain death, and the ethics of diagnosis and treatment of patients who, by definition, have no way to approve of or communicate about their wishes.