Abstract: Cementitious composites suffer from inherent brittleness, low toughness, and limited crack resistance, restricting their performance in complex service environments. Engineered Cementitious Composites (ECC) achieve tensile strain-hardening and multiple cracking through fiber bridging, but PVA and PE fibers differ significantly in interfacial bonding. This review focuses on three aspects: 1) Micromechanical design criteria: coordination of crack-tip fracture and fiber bridging load/energy, considering matrix heterogeneity, defect distribution, and fiber orientation; 2) PVA-ECC design theory: interfacial control of debonding–slip energy distribution and its effect on macroscopic tensile response; 3) PE-ECC model modification: coupled effects of fiber tilt, interface wear, and slip hardening, and strategies for bridging-model adjustments. Unlike previous ECC reviews that emphasize composition and performance, this study systematically compares PVA and PE systems in design-theory evolution and bridging-model modification. Future work should develop bridging models capturing interfacial evolution under age, environment, and multi-field conditions, integrating friction, slip, fiber tilt, and damage into a unified micro–macro framework to enhance predictive consistency and engineering applicability.