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This chapter examines the understanding of dynamic fracture processes based primarily on experimental results, with purely analytical treatments taking on a decidedly secondary character. The specific field of dynamic fracture mechanics is typically characterized in terms of far-field loading and crack-tip local response characteristics that invoke motions strongly influenced by material inertia and high rates of deformation of the material in the crack tip vicinity. These latter conditions generate a constitutive response that is significantly different from its quasi-static counterpart. Constitutive behavior that is independent of deformation magnitude and rate is the classical basis for all elastodynamic analyses. Sufficient information has surfaced during the last two decades which explains the significant differences between elastodynamic analyses and laboratory experiments: on the one hand, these discrepancies are the result of the idealization of the fracture process in the analyses, and, on the other, of the truly complicated details accompanying fracture in the small region around the crack tip when a crack propagates rapidly.