Tunneling in karst is a special challenge in many fields. The present master thesis deals with karst in its terminology, it geographical distribution and its genesis. The phenomenon karst appears in many rock types like salt rocks, sulphate rocks and carbonate rocks. The tunnel Steinbühl at the Swabian Alb in the railway network of Deutsche Bahn, is driven through the geological formations of shell limestone and dolomite rocks. These geological conditions require special site investigations and methods for karst investigations. The karst investigations can be done by direct exploration, like drilling including recording of the drilling parameters, or indirect exploration by geophysical methods, like electrical resistance measurement, ground penetration radar, seismic survey and gravity measurements. A good concept for karst investigation is basis for constructing tunnels with smooth processing. Not only the site investigation is influenced by the karst, but also the planning, the dimensioning and the manufacturing of the inner lining is affected. Karst geology requires a good teamwork of all project partners and special contractual requirements. Finally there are some suggestions given, that could help realising tunnelling projects in karst easier.