Of the many forms of land degradation soil erosion by water is the most serious. Erosion may have significant on-site impacts e.g. for the farmer, but in many areas, off-site impacts are greater. These include, sedimentation of reservoirs and lakes, pollution of freshwater systems and muddy flooding of property. Assessment of erosion is achieved by monitoring, modelling and experimentation. Mitigation measures are well known but require societal support – usually subsidies. Land degradation is a global problem but is acute in several ‘hotspots’ such as east Asia and China, Madagascar and Ethiopia.