The book relates experience of TBM drives in difficult geology, making use of case studies from Turkey to demonstrate the influence of the local geotechnical conditions on the selection of a tunnel boring machine and the selection of tools. There is an extensive description how various geological phenomena, such as for example transition zones, dikes, rock discontinuities, blocky ground, squeezing ground, swelling clays and high strength and abrasive rocks, can reduce the advance rate and what countermeasures can be introduced. There is also a discussion of necessary advance probing and safety measures. Since the presented practical experience from Turkey can also be applicable for other tunnel projects in difficult geology, the book represents a valuable source of knowledge for every tunneler.