One of the major reasons for composite failure is a breakdown of the bond between the reinforcement fibers and the matrix. When this happens, the composite loses strength and fails. By engineering the interface between the natural fibers and the matrix, the properties of the composite can be manipulated to give maximum performance. Interface engineering of natural fiber composites for maximum performance looks at natural (sustainable) fiber composites and the growing trend towards their use as reinforcements in composites.Part one focuses on processing and surface treatments to engineer the interface in natural fiber composites and looks in detail at modifying cellulose fiber surfaces in the manufacture of natural fiber composites, interface tuning through matrix modification and preparation of cellulose nanocomposites. It also looks at the characterization of fiber surface treatments by infrared and raman spectroscopy and the effects of processing and surface treatment on the interfacial adhesion and mechanical properties of natural fiber composites. Testing interfacial properties in natural fiber composites is the topic of part two which discusses the electrochemical characterization of the interfacial properties of natural fibers, assesses the mechanical and thermochemical properties and moisture uptake behavior of natural fibers and studies the fatigue and delamination of natural fiber composites before finishing with a look at Raman spectroscopy and x-ray scattering for assessing the interface in natural fiber composites.