This document provides guidelines for the physico-chemical characterization of manufactured nano-objects and their aggregates and agglomerates larger than 100 nm (NOAA) subjected to toxicological testing. Given the diversity of seemingly similar compositions by which NOAAs can be produced, accurate physicochemical characterization is essential for the proper identification of test materials and for understanding the toxicological impact of nanomaterials. This document will be useful to anyone (toxicologist, ecotoxicologist, legislator, health and safety professional) interested in the evaluation and interpretation of the potential toxicological effects of manufactured NOAAs.