In the first part of this article, a short definition of geothermal energy is made and geothermal fields are classified according to their enthalpies. In the second part, general uses of geothermal energy and also the geothermal potential of Turkey and especially of western Anatolia are mentioned. Then, the general geology of the study area moving from three example geothermal fields is depicted and supported by lithological columns. The tectonic structure of our study area, western Anatolia, is profoundly explained and the presence of geothermal fields in this area is backed up by geophysical findings in detail in the final section.