For over 40 years, the research on incretin and glucagon has been extended and still advanced globally. Particularly in Japan, many researchers and/or colleagues in this field have investigated their distributions, characteristics, physiological actions and pharmacological potentials and have gotten results prior to overseas researchers. Very recently, the clinical indications and evaluations of the efficacy of DPP-4 inhibitors and/or GLP-1 receptor agonists have added in turn new information into the research field of incretin/glucagon. In the next decade, it would be expected that Japanese young investigators will join and go forward to elucidate the unsolved mysteries.