The Gas and Humidity Standards Group develops and supplies various kinds of gas standards metrologically traceable to the International System of Units as well as humidity standards ranging from trace amounts at ppb level of moisture to high humidity at a dew point of 95 °C. For these standards, this group conducts studies on the preparation methods of gas standards based on high-precision mass measurement and high-sensitivity spectroscopy via cavity ring-down spectroscopy (CRDS). This group also develops gas standards for greenhouse and related gases, which are topical issues, in cooperation with other observational institutes in Japan.