A wide ranging study has been carried out of the forms and mechanisms of failure in solid spheres impacting hard, plane solid surfaces over a range of diameters, impact speed and impact angle. Results illustrated here include examples of soda-lime glass and PMMA. In general the forms of failure observed vary with impact velocity. However, although there is a range of low velocity forms, most materials tend towards a common high velocity form. At the highest velocities, propagating fracture fronts appear as the mechanism of comminution of glass spheres into fine fragments. The dynamic processes behind these velocity variations are discussed in this paper, as well as the influence of material properties.