Carbon nanotubes are considered the allotropes of carbon which are made of graphite. Carbon nanotubes are cylindrical, having a nanometer scale in diameter with several millimeters in length. Because of its small size and mass, it has significant structural, mechanical, and electronic properties. At the same time, the other properties include enhanced mechanical strength with increased thermal and electrical conductivity. Carbon nanotubes have been used as additives for various structural materials in various fields, including optics, plastics, electronics, and other fields of nanotechnology. CNTs have absorbent molecules and cylindrical pores which interact with carbon atoms on the surrounding walls. CNTs also have better environmental and chemical stability with increased thermal conductivity. Because of its small size and significant physical properties, it has become a promising material to be used in various applications. CNTs prevail in two forms, i.e., single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) and double-walled carbon nanotubes (SWNTs). Because of its high thermal conductivity, which is used to enhance thermal conductive never fluids. The increase in thermal conductivity is because of suspended CNTs in conventional heat transfer fluids. CNTs possess ultimate high strength fibers because of which SWCNTs are often compared with steel. They also possess increased resistance against damage due to physical forces. CNTs are also used for Raman and photoacoustic imaging. SWCNTs have a significant potential for photodynamic therapy. CNTs have a strong good option affinity against environmental contaminants. CNTs can be used for gene therapy, tissue regeneration, and the diagnosis of different diseases. Due to the intrinsic properties of CNTs, it is considered the desired material to be used as electrodes in batteries and capacitors. The applications of CNTs involve nonporous filters, catalyst support, and coatings. Single-walled nanotubes are the preferred material for miniature rising electronics.