The assessment and mapping of flood risk involves many different sources of uncertainty. Many of these sources of uncertainty involve epistemic uncertainties that are not necessarily easy to represent statistically. This can create problems for communication between analyst and users when uncertain flood risk maps are being prepared. It is suggested that one way of dealing with this problem is to define Guidelines for Good Practice in the form of a set of decisions that must be agreed and recorded for later evaluation and review. The Catchment Change Network (CCN) is a knowledge transfer project, funded by the UK NERC, that aims to bring academic research and practitioners together to produce guidelines for good practice for uncertainty estimation in predicting the future in the areas of flood risk, water quality and water scarcity all of which involve important epistemic uncertainties. The paper will set out the background to developing Guidelines for flood risk mapping and give an application to a site in Yorkshire, UK.