The fourth edition of this text constitutes a continuation of 20 years of coverage of traumatic brain injury, and broadens the discussion of acquired brain injury. Within TBI, the paradigm shift from an injury occurring at a point in time to a disease entity of a chronic nature is changing the discussion of diagnosis, management, treatment and outcome assessment. Disease specification that differentiates TBIs by the mechanism of injury, the exact nature of the injury, the extent of injury, presence of co-morbidities and their exact nature, gender, age, race, and genome are emerging as crucial. Disease differentiation has impacted diagnosis, treatment and outcome.