From the beginning, man has been modifying natural products with additives of one kind or another. With the advent of plastics and the wide range of fillers and reinforcements that have become available, modifications can be as precise as the tailored resins themselves. This review paper discusses the subject under headings - fillers or reinforcements; factors affecting performance; natural organics; synthetic organic; carbon and graphite; inorganic reinforcements, silicates; glass fillers and reinforcers; other glass reinforcements; other inorganic fillers; metallic reinforcers; metallic oxide fillers; biodegradable fillers; other fillers.