The impact strength of annealed interfaces between high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) and some ethylene-co-vinyl acetate (EVA) and ethylene-co-acrylic acid (EAA) copolymers was obtained using the Notched Izod test. The impact strengths of EVA-HDPE, EVA-LDPE, and EVA-PP interfaces using EVA copolymers with 9 to 27.5 wt % vinyl acetate (VA), and of EAA-PP interfaces using EAA with 3 to 20 wt % acrylic acid (AA), were all equal to or greater than those of the homopolymer used. However, the impact strengths of EAA- HDPE and EAA-LDPE interfaces were all lower than those of pure HDPE or LDPE, with the exception of 3EAA-LDPE. Scanning electron micrographs showed the presence of fibrils and/or voids, mostly on those copolymer-homopolymer fracture surfaces which had high impact strength. X-ray photoelectron spectroscopy of the fracture surfaces showed a greater calculated percentage of AA or VA on both the copolymer and homopolymer sides of the interface than in the bulk for most samples at 15 Angstrom penetration. This greater calculated percentage of AA or VA is probably due to chain scission during sample preparation or fracture, which results in additional acid or alcohol groups at the surface that are calculated as increased VA or AA content.