Nanocomposites are a form of nanomaterial consisting of one or more nanoscale phases embedded in a ceramic matrix, metal, or polymer matrix.. The structure of traditional particle-reinforced composites is drastically replaced by the nanostructure created by adding discrete nanoparticles into a continuous solid matrix.. The author of this article discusses nanocomposites, including their structure, classification, preparation process, applications, and potential future development. Over the course of the last twenty years, nanocomposites have become a novel class of materials that have drawn a lot of attention from researchers and engineers. When nanoparticles are less than 5 nm in size, catalytic activity in nanocomposite systems is triggered; when they are less than 20 nm, hard magnetic materials are softened; when they are less than 50 nm, refractive index changes are produced; when they are less than 100 nm, superparamagnetism and other electromagnetic phenomena are produced; and when they are less than 100 nm in the same range, strengthening and toughening are enhanced. Following the recent discovery of carbon nanotubes (CNTs), a novel and intriguing property has been introduced to this field, opening the door to the possibility of using CNTs to produce nanocomposites with improved thermal, electrical, and mechanical characteristics. Based on the matrix materials, nanocomposite materials can be categorized into three groups: Metal Matrix Nanocomposites (MMNC), Polymer Matrix Nanocomposites (PMNC), and Ceramic Matrix Nanocomposites (CMNC).