The definition of nanotechnology may be given based on the perspective of Richard P. Feynman, who foresaw the potential of small-scale science. He asked “ […] what would happen if we could arrange atoms the way we want […]” in his revolutionary paper “There is Plenty of Room at the Bottom”,¹  wherein he touched on the possibilities that could be brought about by the atom-by-atom manipulation of materials. Nanotechnology is a diverse and multi-disciplinary field that covers study and research on phenomena, materials, systems, and operations on the nanometre scale. Nanoparticles are ultra-fine materials at a size range on the order of nanometres (∼10⁻⁹ m), and in general, defined as particles of 1–100 nm in size, although the need to treat sub-micrometre-sized particles (particularly smaller than the lower limit of the wavelength of visible light) is emphasized.²  The term nanofluids refers to the mixing of nanoparticles and common industrial fluids (i.e., base fluid), to obtain properties much better suited to applications than those of base fluids alone. The term nanofluids was coined by Choi and Eastman,³  who stressed that nanofluids were “the best hope for enhancement of heat transfer” due to their higher thermal conductivities compared to those of common industrial liquids. The main focus of this chapter is the use of nanofluids in heat transfer applications, and possible environmental, health-related, and socio-economic outcomes that may potentially be brought about by the use of nanofluids. With this motivation, this chapter aims to draw a realistic picture showing both the promising and challenging points in the path to nanofluid industrialization.