Fibroblast growth factor and FGF receptor (FGFR) system play significant roles in many biological events including pattern formation in many tissues during vertebrate embryogenesis at early stages. The functions of each of FGFs and their receptors have recently been revealed by a variety of approaches among species. We have recently generated FGF10-deficient mice by gene targeting. This KO mice had complete truncation of the fore-and hindlimbs and with no lung. Analyses of the embryos and marker gene expression showed that FGF10 triggers sequential events, which are essential for formations of limb and lung. Focusing on FGF10 function, the FGF-FGFR system is discussed.