Soil degradation threatens soil health in terms of soils functioning as complex living biological systems, delivering multiple ecosystem goods and services. For example, soil erosion removes the most fertile topsoil, reducing soil depth and soil health, which leads to poor crop growth. This impacts on the economic sustainability of farmers’ livelihoods. This chapter identifies different types of soil degradation, focusing on soil erosion by water. Soil erosion processes are described, and how these change soil properties that relate directly to crop growth, including soil depth, water-holding capacity, biota, carbon content and nutrient reserves. The causal links between soil erosion and crop production are presented, including attempts to quantify the economic costs incurred. It is likely that current impacts and costs will increase further under climate change, increasing the need for effective soil erosion mitigation measures that also enhance soil health.