A large amount of research has emerged utilizing bio-fibers for composites reinforcement. A significant component of the research has been directed towards compatibilizing the surface of the natural fibers with the polymer matrix through chemical treatments. These chemical treatments include alkaline, silane, isocyanate and acetylation treatments. As with other continuous fiber composites, the strength and modulus enhancement are strongly anistropic with the greatest increases observed in directions parallel to the fibers. Most of the engineering polymers reinforced with natural fibers show an increase in the tensile strength and young’s modulus, in the fiber axial direction, usually at significant fiber weight percentages. However, the increase in much more modest in comparison with synthetic fibers. Numerous factors affect the mechanical enhancement of natural fiber composites; from chemical treatments and processing methods to environmental conditions. A particular note on the environmental conditions; the large amount of hydrophilic groups on the natural fibers causes them to be hygroscopic. This results in swelling of the fiber and can degrade the composite properties. Natural fiber composites also show improvements in the viscoelastic properties of the composites such as the storage modulus across the glass transition.