Publisher Summary Genetic factors play an important role in the pathogenesis of osteoporosis. Apart from this, genetic factors also play a key role in regulating other phenotypes that predispose to osteoporotic fractures such as the ultrasound properties of bone, biochemical markers of bone turnover, and femoral neck geometry. This chapter reviews the strategies that have been used to identify and quantitate genetic influences on osteoporosis and then goes on to discuss how these approaches have been applied to define candidate loci and genes that predispose to osteoporosis. Many candidate gene associations in the osteoporosis field are based on single studies with relatively small sample sizes that have not been replicated in different populations. These candidate genes include collagen type I alpha 1 (COL1A1), estrogen receptor alpha (ESR1), lipoprotein receptor-related protein 5 (LRP5), transforming growth factor beta 1 (TGFB1), and vitamin D receptor (VDR). These are explained in detail in this chapter. A large number of other candidate genes have been studied in relation to BMD and susceptibility to osteoporotic fracture and these are summarized. This chapter also highlights the gene–gene interactions that play a role in bone mass determination. Finally, it highlights the implications of the studies on the genetic basis of osteoporosis on clinical practice.