During this webinar Dr. Thomas Andersen will discuss how thousands of bone remodeling units (BRUs) constantly renew our bones throughout our lives. These units are also known as basic multicellular units (BMUs) and involves a highly coordinated bone resorption and formation. This webinar will cover the recently revised phases of the BMUs and the key cellular organization within these phases. These phases include: i) an activation phase that lead to the recruitment and activation of osteoclasts; ii) an initial resorption phase where primary osteoclasts initiate the erosion; iii) a reversal-resorption phase where secondary osteoclasts further expand the erosion, while intermixed osteoblastic reversal cells (osteoprogenitors); and iv) a formation phase where osteoblasts refills the resorption cavity. The webinar will especially focus on the bidirectional cross talk between osteoclasts and osteoprogenitors, which play a pivotal role in the activation of osteoclastic bone resorption and its transition to osteoblastic bone formation. Furthermore, the webinar highlight how a combination of molecular histology and histomorphometry have facilitated these recent advances.