This chapter discusses gene-disease associations in osteoporosis. Osteoporosis is - together with osteoarthritis - the most common locomotor disease, and its clinical sequela, including fractures, cause substantial disease burden and costs. It has strong genetic influences, and identification of the underlying DNA variants can help in understanding the disease process and might benefit the development of interventions and diagnostics. The GENOMOS and GEFOS consortia have been established, using large collections of DNA samples from subjects with osteoporosis phenotypes that use standardized methodology and definitions. These collaborative consortia have identified - and refuted - associations of well-known candidate genes, and also play an important role in validation of risk alleles from genome-wide association studies (GWAS) for osteoporosis. Together with studies on rare variants, the GWA approach, in combination with the GENOMOS/GEFOS consortia, will help in clarifying the genetic architecture of complex bone traits such as bone mineral density (BMD), and - eventually - in understanding the genetics of fracture risk, the clinically more relevant but biologically more challenging endpoint in osteoporosis.