In this chapter, two case studies from Turkey, the Uluabat hydropower tunnel and T 26 high-speed railway tunnel; one from Taiwan, the Hsuehshan road tunnel, and one from the Venezuela Yacambu Quibor water conveyance tunnel were given to clarify when and why the tunneling method is changed during the progress of the job operations. Uluabat hydropower project started with drill and blast and changed to TBM tunneling due to the metadetritics and graphitic schist leading to high deformations in the tunnel. 11,465 m long tunnel finished in 8 years. T26 high-speed tunnel encountered rock formations with the same geotechnical characteristics as the Uluabat tunnel. The tunnel started with drill and blast and later switched to TBM tunneling. After the collapse of the tunnel, TBM was buried, and tunneling was carried out with drill and blast. This tunnel of 6100 m in length was completed in 13 years. The excavation of the Hsuehshan tunnel, 12.9 km in length with two-lane tunnels and a pilot tunnel, was started with 3 TBMs. After a complex geology with several water-bearing faults, the tunnel was carried out with drill and blast. The project began in 1974, but it took 34 years to complete for technical, political, and financial reasons. Over those 34 years, the project was stopped and started again eight times using TBMs, roadheaders, and conventional tunneling methods. Given the selected case studies, the need for detailed geological studies and proper selection of the Tunneling method are emphasized.