This document provides guidance for the methods to address dissolution rate and dispersion stability for nanomaterials with focus on environmental aqueous media. The definition of nanomaterials as having one dimension between 1 and 100 nm is generally accepted. The guidance provided here is relevant for solids in the nanoscale as well as their aggregates and agglomerates and it focuses on their fate and behaviour in aqueous media. In particular it presents the influence of various experimental conditions on the performance and outcomes of the discussed methods. In addition, this GD addresses modifications or additions to the methods and aims to give support for the interpretation of the test results.