For an economic analysis and design of geothermal facilities a well-founded knowledge of the relevant thermal subsoil properties is indispensable. Therefore, the Geothermal Response Test (GRT) is a reliable and effective field investigation procedure. With this contribution the authors present fundamentals of the testing procedure and discuss new enhancements of the Geothermal Response Test in order to promote the application of the Geothermal Response Test into a standardized testing procedure and hereby to emphasize the practical usage of geothermal energy.