Osteoporosis is a serious disease with high morbidity and mortality due to atraumatic fractures. In the pathogenesis of osteoporosis, in addition to environment, endocrine imbalance and genetic background are also in play. However, bone alone modulates a number of extra-skeletal systems. In the monograph attention is focused in hormones and genes regulating bone homeostasis, as well as in bone circuits, which modulate systemic endocrine and metabolic regulations, e.g. insulin secretion, glucose metabolism or male reproduction. Candidate genes for osteoporosis are classified according to metabolic and hormonal pathways, which regulate bone mineral density and bone quality. In the book practical utilization of pharmacogenetics (identification of single candidate genes using PCR) and pharmacogenomics (using genome wide association studies) to choose optimal treatment for osteoporosis is discussed.