Fillers having particle sizes between one and one hundred nanometers are known as nanofillers (e.g., carbon blacks and synthetic silicas). Different nanofillers have recently entered the market, including needle-shaped nanowhiskers and nanoclays (montmorillonite, smectite). Both inorganic and carbon-based nanofillers are used. Additionally, polymers are mixed with inorganic and carbon-based nanofillers. Top-down approaches and bottom-up procedures are the two basic fabrication techniques for nanofillers. Lithographic processes, arc discharge, laser ablation, ball milling, and inert gas condensation are examples of top-down approaches. Electrospinning, hydrothermal synthesis, sol-gel, electrochemical, molecular beam epitaxy, chemical vapor deposition (CVD), microwave, and homogeneous nucleation are some of the bottom-up techniques. Numerous attempts have been undertaken to mechanically or chemically create different kinds of inorganic nanoparticle-filled polymers (filler/polymer nanocomposites). These methods, however, necessitate altering the nanofiller surfaces and/or difficult polymerization processes, rendering them unsuitable for the manufacturing of nanocomposites on an industrial scale. These chapters provide in-depth details on the many ways that nanofillers are synthesized and fabricated. Additionally, the information in these chapters covers various kinds of surface modification techniques as well as surface modification techniques for nanofillers.