Predictions of water availability across large regions are required so that water managers and policy makers can adequately plan for current and future water availability and water use. A major issue in making such predictions is that, in general, only some catchments are gauged and thus estimates of discharge must also be made for large ungauged areas. Numerous techniques have been developed to make these estimates, with most relying on some sort of hydrologic regionalisation. This session invites papers which examine how best to regionalise hydrologic response into ungauged areas, with a particular focus on assessing the uncertainty in the regionalised predictions.