FRAX is a computer-based algorithm that provides models for the assessment of fracture probability in men and women (http://www.shef.ac.uk/FRAX). The approach uses easily obtained clinical risk factors to estimate 10-year fracture probability, with or without femoral neck bone mineral density (BMD), to enhance fracture risk prediction. It has been constructed using primary data from population-based cohorts around the world. The gradients of fracture risk have been validated in independent cohorts with a similar geographic distribution. The FRAX tool should not be considered as a gold standard, but rather as a platform technology on which to build as new validated risk indicators become available. Notwithstanding, the present models provide an aid to enhance patient assessment by the integration of clinical risk factors alone and/or in combination with BMD. This article describes the steps undertaken in the development of FRAX.