The clinical, biochemical, and genetic features of both FGF23-dependent and -independent forms of HR are discussed, including X-linked hypophosphatemia (XLH), autosomal dominant hypophosphatemic rickets (ADHR), autosomal recessive hypophosphatemic rickets (ARHR), tumor-induced osteomalacia (TIO), hereditary hypophosphatemic rickets with hypercalciuria (HHRH), and Fanconi syndrome. The gene discussed is FGF23; the disease is X-linked hypophosphatemia.