In our aging population, osteoporosis is a major public health problem. Fragility fractures are associated with significant morbidity, loss of functional independence, and mortality. Bone mass is determined by the balance between bone formation by osteoblasts and bone resorption by osteocytes. A third cell type, the osteocyte, senses external signals to bone and relays this information to nearby osteoblasts and osteoclasts on bone surfaces. The Wein laboratory studies molecular mechanisms controlling osteocyte differentiation and function. To do this, we apply cutting edge technologies to define the circuitry crucial for osteocyte function.