Plant fibers have always found wide applications from the time they gained commercial prominence. Natural fibers tend to absorb considerable amount of moisture which causes deterioration in mechanical properties. The surface of natural fiber is usually modified by physical or chemical treatments in order to make it more compatible with hydrophobic polymers for improved properties of the resulting composite. Modified natural fibers are mostly used for the preparation of natural fiber–reinforced polymer composites. There has been an increased interest in the use of biopolymers in many applications due to their biodegradability, high tensile strength, and modulus. For example, polylactide (PLA) materials have been utilized extensively in packaging and medical applications. In this chapter, the characteristics of reinforcing natural fibers and the polymer matrices will be discussed. Also, the effect of chemical treatment on the mechanical properties and fire resistance of natural fiber–reinforced polymer‐based composites are discussed. Finally, the chapter is concluded with recent and possible future applications of natural fiber composites.