New targeted therapies are needed to improve bone strength. This project will study the cells that are located within the periosteum (exterior surface of cortical bone), using lineage tracing (genetically introduced fluorescent labels), to identify and track periosteal cell populations. We will test how these cells respond to a known treatment that stimulates bone growth. By studying the cells and molecular mechanisms involved, we hope to identify novel targets and pathways that may be used in the future to improve bone strength.