Isolated fibroblast growth factor receptor 5 (FGFR5) polypeptides are provided, together with polynucleotides encoding such polypeptides. Also provided are modulators of FGFR5 gene expression and binding molecules that specifically bind to, and agonize or antagonize, FGFR5 polypeptide function. Binding molecules include antibodies, and functional fragments thereof, as well as scFv and Camelidae heavy chain IgG that specifically bind to FGFR5 thereby modulating the activity of FGFR5. Such binding agents and modulators of FGFR5 gene expression may be employed for the treatment of disorders including: osteopontin-mediated diseases; autoimmune diseases, such as systemic lupus erythematosus; bone disorders such as osteoporosis and osteopetrosis; and cancers, including cellular carcinomas such as hepatocellular carcinomas.