Dual energy x-ray absorptiometry (DXA) is a quantitative imaging procedure for the measurement of bone mineral density and the diagnosis of osteopenia and osteoporosis. In a sporting context, DXA is particularly useful for the evaluation of athletes at risk of relative energy deficiency in sports, a condition associated with overtraining and/or undernutrition. This chapter informs on the safe and effective practice of DXA scanning and provides informed guidelines to promote high-quality standards in DXA scan acquisition and interpretation in sport and exercise sciences research and practice. DXA uses two x-ray beams of different energies that are diversely attenuated by bone and soft tissue. DXA involves a small amount of ionising radiation. DXA has an integral place in sport and exercise sciences, given its unique ability to measure bone, lean and fat mass status concurrently with a high degree of precision.