Fundamental knowledge concerning how thermoplastic polyolefins (TPOs) fail under impact fracture conditions is lacking. Approaches for gaining such knowledge are proposed. The fracture mechanisms in a variety of experimental and commercially available thermoplastic olefins (TPO) blends are investigated using the double-notch four-point-bend Charpy impact test. It is shown that the operative impact fracture mechanisms and the size of the damage zone in TPO blends depend strongly on the impact modifiers utilized. Strategy for improving low temperature impact strength of TPOs is discussed.