This chapter provides an exhaustive examination of the characteristics of various natural and synthetic fibers utilized in the formation of pure natural composites as well as hybrid composites predicated on the amalgamation of both natural and synthetic fibers. It further addresses bio-based resins, a variety of fabrication techniques, the chemical and mechanical properties of fibers, and the impacts of chemical treatment alongside the influence of nanoparticles on composite materials (Atmakuri et al. in Polym 12(9):1–30, 2020 [1]). Natural fibers have garnered increasing interest and esteem among researchers, delivering satisfactory results due to their abundant availability, simplicity of fabrication, cost-effectiveness, biodegradability, and environmental sustainability. Hybrid composites, composed of two distinct natural fibers within the same matrix material, are more prevalent than combinations of natural and synthetic fibers. Contemporary studies concerning natural fiber hybrid composites have demonstrated that, in light of their biodegradability and the influence of the individual fibers' strength on mechanical properties, flame retardancy, and moisture absorption, natural fibers necessitate additional treatments, such as chemical treatment, to overcome these limitations and enhance their properties. The effect of chemical treatment on the thermal, mechanical, and moisture characteristics of composite materials has been investigated. Researchers have identified a favorable impact on overall strength resulting from the incorporation of filler materials (nanoparticles) in composite materials. Hybrid composites represent a central topic in polymer science, attracting significant attention for a range of lightweight applications across a wide array of industries, including the automotive, construction, shipping, aviation, sports equipment, electronics, hardware, and biomedical sectors.