Research on injuries is a high priority to inform public policy that reduces deaths, hospitalizations and associated costs. Principles for research design and analysis of injury incidence and severity are emphasized. Review of extant surveillance data reveals numerous flaws that must be changed to increase usefulness of the data. Research designs of studies of injury causation and evaluation of countermeasures are often inappropriate and mislead analytic and injury control efforts. Appendices to chapters illustrate research projects that influenced public policy affecting the reduction of motor vehicle fatalities per population by half in the U.S. The principles illustrated by these studies can be applied to other types of injury.