Epoxy resins, despite their outstanding mechanical and chemical properties, face serious limitations in high‑durability applications due to their inherent brittleness and low fracture toughness. This paper provides a comprehensive and systematic review of the latest strategies and scientific advances in the heterogeneous toughening of epoxy resins, focusing on the fundamental mechanisms and the quantitative performance of additives such as liquid rubbers, core–shell particles (CSPs), thermoplastics, liquid‑crystal polymers, and nanomaterials. These modifiers dissipate energy and enhance fracture resistance through mechanisms including shear yielding, cavitation, bridging, and crack deflection. Toughening with liquid carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber can improve impact strength by more than 200%, although it typically reduces modulus. In contrast, additives such as thermoplastics and CSPs achieve a desirable balance between toughness and stiffness—for instance, methacrylate‑modified CSPs increased the critical stress‑intensity factor (KIC) from 0.85 to 2.93 MPa·m½ (a 245% rise). Synergistic effects are also evident in hybrid systems; combining rubber and phenoxy raised the critical strain‑energy release rate (GIC) by 260%. In nanocomposites, incorporating 0.5 wt% graphene oxide grafted triblock copolymer (GO–g–TBCP) led to an impressive 397.9% increase in fracture toughness. This study highlights that selecting a toughening approach requires a careful balance between enhancing toughness, maintaining thermo‑mechanical performance, and ensuring process compatibility. The future of this field lies in hybrid systems, bio‑based materials, and smart nanostructures with advanced surface engineering.