Recruitment of osteoblast lineage cells to their bone-forming locations is essential for skeletal development and fracture healing. In developing bones, osteoprogenitor cells invade the cartilage mold to establish the primary ossification center. Similarly, osteogenic cells infiltrate and populate the callus tissue that is formed following an injury. Proper bone development and successful fracture repair must, therefore, rely on controlled temporal and spatial navigation cues guiding the cells to the sites where new bone formation is needed. Some cellular mechanisms and molecular pathways involved have been elucidated.