The four aims of impact biomechanics are (1) Identification and explanation of injury mechanisms (2) Quantification of mechanical response of body components to impact (3) Determination of tolerance levels to impact and (4) Assessment of safety devices and techniques to evaluate prevention systems. These are briefly described followed by a discussion of the methods used to study injury biomechanics. The rest of the chapter is devoted to injury mechanisms which need to be understood if preventative measures are to be developed and implemented. The mechanisms covered are brain injury and acute subdural hematoma, neck pain due to whiplash, aortic rupture, spinal injury due to vertical acceleration, disc rupture, hip fracture in the elderly, ankle (pilon) fracture and foot fracture. It is concluded that much misinformation exists in the literature regarding these injuries and the statement in Lancet (Issue 9773): “The most entrenched conflict of interest in medicine is a disinclination to reverse a previous opinion” is indeed true.