During the last years, there has been an increasing interest in natural fiber-reinforced polymer composites, referred to as biocomposites, which are also referred to as green composites or eco-composites. Industrial natural fibers have been increasingly utilized to fill and reinforce not only conventional thermoplastic and thermosetting polymers but also biodegradable polymers. Their advantages and disadvantages mostly rely on those of natural fibers, which are also referred to as biofibers. Natural fiber reinforcements have a number of merits over conventional glass fiber reinforcement, for example, natural abundance, low cost, low density, environmental friendliness, carbon dioxide sequestration, acceptable specific mechanical properties, damping and insulation characteristics, biodegradability. However, they also have some drawbacks, such as poor natural fiber–matrix interfacial adhesion, fiber variability, surface irregularity, finite fiber length, limited thermal stability, and restricted processing temperature. The strong adhesion or bonding at the interfaces between natural fibers and a polymer matrix is critical to promote the properties and performances of biocomposites. In general, such strong adhesion cannot be established in the biocomposite system using natural fibers if appropriate surface treatment or modification is not performed. Therefore, a large number of studies on chemical and physical surface treatments of various natural fibers have been devoted not only to increasing the interfacial adhesion between the natural fiber and the polymer matrix but also enhancing mechanical, thermal, and other properties of biocomposites consisting of different types of natural fibers and polymers. It is worth overviewing extensively current research efforts on the effects of surface treatment of natural fibers on the properties of biocomposites in terms of interfacial, static mechanical, dynamic mechanical, impact, thermal, physical, morphological, fracture behavior, and water absorption. The present chapter was described focusing mostly on the results reported in recent years.