Natural fibers such as flax, hemp, kenaf, jute, sisal, ramie, and coir are often considered as reinforcing polymers for enhanced performance. Indeed, the stiffness of these fibers in the axial direction is on par with that of glass fibers (for instance, 50-100 GPa stiffness is reported for flax fibers). There are well-known advantages of the use of natural fibers in composites, since they are of low density, have a smaller impact on the processing equipment (in terms of wear), are more environmentally friendly, and, of course, are renewable. Simultaneously, a number of problems hinder a wider use of these fibers in structural composites, namely sensitivity to moisture, large variation of properties, limited length, difficulty to control orientation, and poor chemical compatibility between the fibers and the matrix. In the case of non- or semistructural applications of the natural fiber, common processing methods are used (e.g., injection molding of packages, extrusion of beams for decking, and compression molding of panels for automotive use). These methods tend to produce short-fiber composites. However, recently, more advanced reinforcements based on natural fibers have been developed, such as randomly oriented fabrics, fiber rovings, and noncrimp and woven fabrics. Use of these reinforcements allowed production of composites with a much better mechanical performance. Although assembly of fibers into various types of fabrics somewhat helped solve problems associated with limited fiber length and improved control over fiber orientation, other problems mentioned earlier still remain to be solved. Therefore, the design of natural fiber composites with predefined properties for structural applications and long service life under harsh conditions is very challenging. Development of appropriate models that can describe the complex behavior of natural fiber composites would be a very useful tool for composite designers.