A crucial component to understanding the biomechanics of injury is the study of real world injuries. These studies are essential to characterize the incidence and characteristics of impact injuries, to establish impact test configurations, and to evaluate the effectiveness of injury intervention measures. This chapter will describe the data sources for these evaluations, metrics of performance for injury, and representative applications, i.e., the generation of injury risk curves, measurement of societal costs of injuries, and estimating the mortality associated with specific injuries.