FGF-18 is a member of the fibroblast growth factor family and belongs to the FGF8 subfamily. FGF-18 acts as a pleiotropic factor and stimulates proliferation in many cell types. It has been shown that the injection of recombinant FGF-18 into mice can induce significant cell proliferation in many tissues, especially in the liver and small intestine. Similar to FGF-1 and FGF-2, FGF-18 plays an important role in bone development. Many studies have shown that FGF-18 is an important regulator for both chondrogenesis and osteogenesis. It has been suggested that FGF-18 inhibits chondrogenesis through FGFR3 during embryonic development. FGF-18 knockout mice die early during neonatal period and display elongated zones of proliferating and hypertrophic chondrocytes. Because FGF-18 stimulates chondrogenesis after injury and promotes the repair of damaged cartilages, it has been tested in osteoarthritis clinical trials. In osteogenesis, FGF-18 plays a positive role and stimulates osteoblast differentiation. The expression of FGF-18 is directly regulated by osteoblast transcription factors RunX2 and Wnt3a. In addition, FGF-18 is involved in cortical neuron activity, hair growth, and stem cell differentiation. FGF-18 can be used to promote human pluripotent stem cells into the mature airway epithelia. The participation of FGF-18 in cancer development has been well investigated and it has been identified as a biomarker in ovarian cancer.?