Much of the design and development of the modern automobile is dedicated to protecting occupants or reducing vehicle damage during and after a crash. Although the primary function of the vehicle body structure in this respect is to dissipate the kinetic energy of the vehicle, effective protection depends upon careful management of this energy in order to achieve the optimum collapse mechanism. For conventional metal components, the art of creating such “crashworthy” performance is now well understood. However, more and more vehicles are turning to polymer-based composite materials in their structures and these exhibit a totally different type of behaviour in the way that they dissipate energy to the metals which they replace. This paper reviews the fracture mechanisms of these materials, in relation to different impact speeds, as they affect the vehicle designer.