Coalbed methane is one of unconventional natural gas, such as shale gas and methane hydrate. Shale gas was developed aggressively a few years ago in United States. In Japan, the development of technology for producing methane hydrate has been carried out. Coalbed methane was produced commercially since 1990's in United States and it has been produced continuously. In this paper, detail of coalbed methane such as generation of coalbed methane, measurement of methane contents, resources in the world and production system are described. Finally, resources and development plan in Japan are also described.