The Selby 3D geological model, commissioned by the Environment Agency, covers an area of 1,300km2 and shows the distribution and thickness of superficial deposits between Thorne, just north of Doncaster, to Haxby, just north of York. Surfaces derived from this model will be used by the Environment Agency to construct a numerical, spatially distributed model of recharge to the underlying regionally important Sherwood Sandstone Group aquifer and to update their existing numerical regional groundwater model. This report describes the geological units modelled, the 3D modelling methodology used and the limitations of the model.