Insulin, a peptide hormone produced by pancreatic beta-cells, plays a crucial role in glucose metabolism and regulation. Beyond its well-known effects on hepatocytes, myocytes, and adipocytes, insulin has significant influences on bone metabolism. Both type 1 and type 2 diabetes are associated with increased fracture risk and alterations in bone quality, which cannot be fully explained by bone mineral density alone. Insulin receptors are expressed on osteoblasts and osteoclasts, mediating insulin’s anabolic effects on bone by promoting osteoblast differentiation and modulating bone remodeling. In type 1 diabetes, insulin deficiency leads to reduced bone formation and mineralization, while in type 2 diabetes, hyperinsulinemia may preserve or increase bone density despite compromised bone microarchitecture. Furthermore, bone-derived osteocalcin acts as an endocrine regulator of energy metabolism, linking skeletal health and glucose homeostasis. This chapter provides a comprehensive overview of the interplay between insulin and bone, emphasizing the dual role of bone as both a target and a regulator of metabolic function.