Severity scales to characterize the nature and extent of injury are important adjuncts to trauma care systems, trauma research and many of the elements of a complete public health approach to injury. This article provides a brief overview of severity scale development over the past 30 years during which the science to support such initiatives has matured substantially. Anatomical, physiological, intensive care, composite and complex scales and models now abound and are being applied to a variety of tasks with increasing precision. Trauma registries enable the meaningful aggregation of data for the development and testing of models. Future challenges are identified as are potentially fruitful avenues of research.