 The bone marrow contains two distinct populations of skeletal stem cells, SSCs, one located in the endosteum and another in the stromal compartment. The endosteal population is composed of fibroblast growth factor receptor 3, FGFR3, expressing cells that have characteristics of both bone osteoblasts and chondrocytes. In contrast, the stromal population is composed of lepar expressing cells that are responsible for providing a majority of bone-forming osteoblasts in adult and aged bone marrow. Both populations of SSCs are essential for proper bone development and maintenance. This article was authored by Yuki Matsushita, Jolin Liu, Angel Kaya Yangchou and others.