Gas geochemistry in the last two decades has emerged as an important scientific tool in geosciences due to the significant improvement of instrumentation. A review of recent progress in this field, based on the examples in Taiwan, shows that gas geochemistry is applicable to a wide range of problems in Earth sciences. The International Conferences on Gas Geochemistry (ICGG), held since 1982, are the only international venues exclusively dedicated to studies of gas geochemistry. This thematic edition, which includes 11 case studies presented during the 9th ICGG held in Taipei, 2007, covers a wide range of topics from both on-land and submarine geothermal, seepage ⁄ venting studies to gas flux estimation from mangroves and optimum sequestration depth for CO 2 geological storage.