The IAEA assists its Member States in their efforts to develop effective, evidence based interventions to combat malnutrition in all its forms using nuclear techniques. This publication was developed as an integral part of the IAEA’s efforts to contribute to the transfer of technology and knowledge in the application of a widely used nuclear technique in nutrition, dual energy X ray absorptiometry (DXA). It provides information on the theoretical background as well as on the practical application of DXA to measure bone mineral density and to assess body composition.