Nanomaterials (NMs) have the potential to improve the treatment and diagnosis of disease as they are suitable candidates for a number of diagnostic and therapeutic applications. On entering the body via a variety of exposure routes, and during their translocation to secondary target sites it is inevitable that NMs interact with biological molecules, such as proteins. These interactions may influence the behaviour and toxicity of NMs following exposure. As the surface of NMs is what interacts with cells and tissues it is necessary to identify the influence of NM surface properties on their toxicity, and determine how this is influenced by the route of exposure, and physico-chemical characteristics of NMs. The term protein corona is used to describe the coating of the NM surface with protein. The protein corona is a dynamic and complex structure whose composition is dictated by the biological medium and the physico-chemical properties of NMs (such as their size, composition, hydrophobicity and charge) as this influences protein binding specificity and affinity. Depending on the route of exposure (e.g. inhalation or injection) NMs will encounter different proteins. We have observed that i) the composition of protein corona of NMs is likely to be dictated by their route of entry, ii) the translocation of NMs to secondary target sites may influence the composition of the protein corona (i.e. they encounter different proteins on their transport in the body) so that the composition of the protein corona evolves over time, iii) the physico-chemical characteristics of NMs dictate the composition of the protein corona, and the toxicity of NMs and iv) NMs can affect secondary target sites that vary according to delivery route and corona composition following exposure. These findings, and evidence from the wider literature has therefore led us to hypothesise that NM toxicity is dictated by the exposure route due to the acquisition of a surface coating (protein corona) that is determined by the route of entry and physico-chemical properties of the NM. This information can be exploited within the intelligent design of NMs in the future (e.g. to control protein adsorption and the subsequent cellular response), and be used to improve the design of toxicology investigations (e.g. to inform how NMs should be dispersed within in vitro experiments to more accurately reflect in vivo conditions).