Background: A rich literature exists that has demonstrated adverse human health effects following exposure to ambient air particulate matter (PM), with strong support for an important role for ultrafine (nano-sized) particles. At present, relatively little human health or epidemiology data exists for engineered nanomaterials (NM) despite clear parallels in their physicochemical properties and biological actions in in vitro models. Objectives: NMs are available in a range of physicochemical characteristics which allow a more systematic toxicological analysis. Therefore, the study of ultrafine particles (UFP, <100 nm in diameter) provides an opportunity to identify plausible health effects for NM, while the study of NM provides an opportunity to facilitate the understanding of the mechanism of toxicity of UFP. Methods: A workshop of experts systematically analysed the information available and identified 19 key Lessons that can facilitate knowledge exchange between these discipline areas. Discussion: Key lessons range from the availability of specific techniques and standard protocols for physicochemical characterization and toxicology assessment, to understanding and defining dose and the molecular mechanisms of toxicity. This review identifies a number of key areas where additional research prioritisation would facilitate both research fields simultaneously. Conclusion: There is now an opportunity to apply knowledge from NM toxicology and use it to better inform PM health risk research and vice versa.