This is the first of two chapters dealing with some 60 years of accumulated knowledge in the field of impact biomechanics. The regions covered in this first chapter are the head, neck, and thorax. The next chapter will discuss the abdomen, pelvis, and the lower extremities. Although the principal thrust of the research has been toward the mitigation of injuries sustained by automotive crash victims, the results of this research have applications in aircraft safety, contact sports, and protection of military personnel and civilians from intentional injury, such as in the use of nonlethal weapons. The reader should be keenly aware of the wide variation in human response and tolerance data in the cited results. This is due primarily to the large biological variation among humans and to the effects of aging. Average values are useful in design but cannot be applied to individuals.