This chapter focuses on how surface modification alters the fiber surface and impacts composite properties, with emphasis on potential commercial applications. Drzal et al. believe that the effect of surface treatment is to remove a weak outer layer on the fiber surface and to increase the number of surface active groups, and that it has relatively little effect on the BET surface area. Kozlowski and Sherwood found evidence for a chemical reaction between fiber surface and Epon 828-resin in acidic electrolyte anodic oxidation but concluded that it was not possible to decide whether chemical bonding is responsible for increased interlaminar shear strength of composites produced from treated fibers. Electropolymerization involves the polymerization of monomers in an electrolytic cell; electrodeposition utilizes the migration of preformed polymers or other materials carrying ionizable groups to the oppositely charged electrode. The literature is replete with correlations between various surface analysis techniques and the fiber-matrix interactions.