Nanomaterials have significant applications in different fields as well as energy, environment, food industry, medicine, and so on. Nanoparticles gain lot of attention because of their unique physicochemical properties like optical, chemical, mechanical, and electrical properties. As a result, changes in specific surface area provide great value and influence critical parameters such as surface reaction. There are certain metals that have distinctive properties; for example, gold and silver contain antimicrobial properties. Metal nanoparticles are used in biomedicine and other fields all around the world. Because of their unique properties, researchers are actively focusing on the fabrication of metal nanoparticles, nanostructures, and nanomaterials. These days, scientists are adding new substances known as nanofillers, such as polyhedral oligomeric silsesquioxane (POSS), nano titanium oxide, nano silica, and nano alumina. The fillers with particle sizes of 1–100 nm range are nanofillers. Nanofillers can work as additives. The mechanical and barrier characteristics may be improved. It aids in preserving the ideal density of the nanocomposite materials while also enhancing several aspects, including thermal, flame retardancy, water retardancy, and mechanical behavior. Due to its greater aspect ratio, surface area, and superior characteristics, nanomaterial applications are expanding in many fields. The present chapter covers the many kinds of nanoparticles, their production process, their benefits and drawbacks, and their applications. The varieties of nanofillers, their characterization, and a brief summary of the main functional characteristics of nanocomposites with respect to their applications are also included.