While nanotechnology and the production of nanoparticles are growing exponentially, research into the toxicological impact and possible hazard of nanoparticles to human health and the environment is still in its infancy. This review aims to give a comprehensive summary of what is known today about nanoparticle toxicology, the mechanisms at the cellular level, entry routes into the body and possible impacts to public health. Proper characterisation of the nanomaterial, as well as understanding processes happening on the nanoparticle surface when in contact with living systems, is crucial to understand possible toxicological effects. Dose as a key parameter is essential in hazard identification and risk assessment of nanotechnologies. Understanding nanoparticle pathways and entry routes into the body requires further research in order to inform policy makers and regulatory bodies about the nanotoxicological potential of certain nanomaterials.