This paper examines the issues of mining gassy coals. These cover a huge range of coal types, gas contents, permeabilities and diffusional behaviour. The key to understanding what approach to take to mining, is an understanding of the geology and the correct measurement of the important parameters. This must be followed by suitable interpretation and a flexible mining approach to dealing with the geology, geotechnical and reservoir conditions. The paper describes some of the techniques used in exploration to define these parameters.