The physical, chemical and biological properties of various nanomaterials differ substantially - as do the potential risks they pose. We argue that nanomaterials must be categorized based on the location of the nanoscale structure in the system/material before their hazards can be assessed and propose a categorization framework that enables scientists and regulators to identify the categories of nanomaterials systematically. The framework is applied to a suggested hazard identification approach aimed at identifying causality between inherent physical and chemical properties and observed adverse effects reported in the literature. We tested the workability of the proposed procedure using nanoparticles as an illustrative case study. A database was generated noting the reported inherent physical and chemical properties of the nanoparticles tested and the main effects observed. 428 studies were noted in the database reporting on a total of 965 nanoparticles. We found that although a limited number of studies have been reported on ecotoxicity, more than 120 and 270 have been reported on mammalian toxicity and cytotoxicity, respectively. In general there was a lack of characterization of the nanoparticles studied and it was not possible to link specific properties of nanoparticles to the observed effects. Our study shows that future research strategies must have a strong focus on characterization of the nanoparticles tested.