This book comprehensively and systematically introduces the microstructure characteristics of plant fibers and the manufacturing process, interface characteristics, mechanical behaviors and physical properties of plant fiber reinforced composites, as well as their engineering demonstration applications. Plant fibers derived from natural resources have been thrust into the global spotlight as environment-friendly materials with attractive advantages of renewability, biodegradability, high specific strength and modulus and good sound absorption and heat insulation performance, and have become promising alternative to traditional synthetic fibers in making fiber-reinforced composites with structure-function integration. This book combines the basic theory with engineering applications for highlighting the unique research method for plant fiber reinforced composites with hierarchical structure. It is intended for undergraduate and graduate students who are interested in natural fiber composites, and scientific researchers and engineers looking to develop the design and manufacture of green composites in the fields of aerospace, railway transportation vehicles, automotive engineering and civil infrastructures.