In recent decades, nanoscience and nanotechnology have prompted great scientific interest and become a flourishing field in science and technology. Advent of nanotechnology has opened many newer niches in the domain of material science. Materials in nano-regime exhibit unique properties which have immense potential for wide ranges of applications. In this quest, numerous nanomaterials have been studied in last few decades. Nanomaterials of different dimensions such as nanoparticles, nanofibers, nanoribbons, nanosheets, nanoclusters, etc. impart tremendous improvement of properties particularly when used as fillers. Nanofillers have taken over the field of materials science by judiciously replacing the conventional fillers. It has been well understood by the scientific community that use of nanofillers in composites, particularly in polymeric nanocomposites, can help in overcoming the serious concerns such as opacity, brittleness, toxicity, and many more. Further, zero-dimensional nano-sized particles offer an enormous amount of surface area and a great dispersion behavior. So, the use of nanoparticles and nanofillers are very promising to attain excellent material behavior. This chapter presents the description of a wide range of nanoparticles and nanofillers, depending upon their dimensions. The different advanced tools and techniques used for the characterization of these nanomaterials have been described herein. This chapter shows different strategies used for the preparation of nanofiller-based composites. This also puts a focus on the improvement of significant properties of materials upon incorporation of nanofillers. Various applications of nanofiller-based composites have been elaborately discussed in this chapter.