This report describes the scientific background, relevant preliminary considerations and experimental work performed for the development of a future ⁠OECD⁠ Test Guideline on determining solubility and dissolution rate of nanomaterials in aqueous environmental media. It gives insight into the derivation of the various test approaches considering relevant environmental conditions and the validation of these within the framework of an international ring test. Upon adoption, the Test Guideline “Determination of the Solubility and dissolution rate of nanomaterials in aqueous media” will be available at the webpage of the OECD Test Guidelines Programme.