Manufactured nanoparticles (MNP) represent a growth area in industry where their interesting and useful properties bestow advantage over conventional particles for many purposes. This review specifically addresses the potential for lung cancer in those who might be exposed to airborne MNP. There is no strong evidence that MNP are carcinogenic and MNP come in a wide spectrum of materials, sizes, shapes and compositions and it is likely that the hazard will vary across different MNP types dependent upon their intrinsic properties. Low toxicity low solubility (LTLS) MNP are unlikely to pose a substantial cancer risk as they are not very biologically active. Nanoparticles with a more reactive surface may undoubtedly generate inflammation more readily and inflammation could be sufficiently intense to lead to secondary carcinogenesis via the oxidants and mitogens produced during inflammation. There is some evidence in vitro that MNP can gain access to the nucleus and the genetic material if specifically designed to do so by surface modification and that nanoparticles such as carbon nanotubes (CNT) can cause genetic aberrations by a primary mechanism additional to the inflammation–mediated one; these potential mechanisms require further study. High aspect ratio nanoparticles (HARN) are MNP that are fibre-shaped and analogously to asbestos might pose a special cancer hazard to the lungs, pleural and peritoneal mesothelium. Recent research suggests that the existing fibre pathogenicity paradigm is adequate for describing the hazard of HARN and that making the HARN of a non-biopersistent material or restricting the length could, via benign-by-design principles, allow safe HARN to be produced.