Current concerns about the impacts of soil erosion on crop productivity and the environment, as well as the deployment of effective soil conservation measures, have generated an urgent need to obtain reliable quantitative data on the extent and actual rates of soil erosion to underpin sustainable soil conservation strategies. The quest for new approaches for assessing soil erosion to complement conventional methods has led to the development of methodologies based on the use of fallout radionuclides (FRNs) as soil erosion tracers. With increasing attention being paid to land degradation worldwide, this publication explains and demonstrates FRN based methods to trace soil movement and to assess soil erosion at different spatial and temporal scales, and to evaluate the effectiveness of soil conservation strategies to ensure sustainable land management in agricultural systems. This publication summarizes the experiences and knowledge gained since the end of the 1990s.