The NIA attended the WPMN 23 meeting at the OECD in Paris from 26-28 June where updates were presented and step foward actions discussed regarding the adaptation of OECD guidelines to nanomaterials, together with the status of the OECD SG on SSIA and on AdMa. The released updated guidelines were the OECD TG 126 on the Determination of the Hydrophobicity Index of Nanomaterials through an affinity measurement and the OECD TG 125 on Nanomaterial Particle Size and Size Distribution.