Polymer composites and nanocomposites reinforced with various microfillers and nanofillers are extensively exploited for an array of commercial applications. However, the paradigm has shifted towards bioprospecting of green nanofillers from various natural sources to prevent fossil fuel depletion, reduce the environmental impact of the production process, and improve material sustainability. The nanofillers are generally added to the polymer matrix as additives in the form of nanoparticles, nanocrystals, nanofibers, nanotubes, etc. The reinforcement of polymer/hybrid nanocomposites with nanofillers improves functionalities such as mechanical strength, thermal stability, UV shielding, flame retardancy, impact resistance, corrosion resistance, electrical resistance, barrier, tribological, recyclability biocompatibility, biodegradability, low cytotoxicity, antimicrobial, and antioxidant properties, which are accountable to large surface area and better aspect ratio of nanofillers. The current chapter briefly focuses on different available natural sources, types of green nanofillers, composition, properties, and their applications in different industrial sectors. The natural sources and green nanofillers, such as clay, carbon, silicon dioxide, calcium carbonate, cellulose, plant nanofibers, chitosan, protein, hydrocolloid gum nanoparticles, etc., are summarized in the present chapter. The green nanofillers serve as sustainable and environment friendly materials for various industrial applications, including packaging (agriculture, food, and beverage), automotive composites, aerospace, building construction materials, consumer goods (disposable plates and cutlery), biomedical implants, soil amendment and conditioner, etc. The success of nanofillers towards industrial applications depends upon quantity and quality of raw materials, supply and process amenability, etc. Further studies are envisaged on development of sustainable and safe production methods, their characterization, properties, performance, benefits, and nanotoxicity of green nanofillers.