The impact performance and resistance of toughness-tailored polypropylene (PP) impact copolymer (ICP) blends were examined using a range of microscopic techniques. The double-notch four-point bending (DN-4PB) Charpy impact technique was used to clearly study the impact-enhancement of the ICP blends responsible for the observed toughening effect. The incorporation of ethylene-octene copolymer with a lower molecular weight into the PP matrix induced the formation of massive crazes and shear yielding, leading to a more ductile PP matrix. A detailed investigation showed that well-oriented talc particles act in the PP matrix as stress concentrators to initiate massive crazes by crack deflection and bifurcation. These toughening mechanisms are responsible for the improved impact resistance. The DN-4PB Charpy impact technique used in this study provides an effective methodology for probing the impact fracture mechanisms of toughness-tailored ICP blends.