The field of high atomic number nanoparticle radiosensitising agents is reviewed. After a brief discussion of the new mode of physicochemical action implied by irradiation of high atomic number nanoparticles embedded in biological systems, a series of exemplars are discussed.Silver-, gallium-and gold-based nanoparticles are discussed in order of increasing atomic number with functionalization strategies being outlined. In-vitro and in-vivo evidence for radioenhancement and the mechanisms attributed to the increased biological effect are discussed.