The destabilizing effect of groundwater is one of the major causes for landslides, which represent a major hazard to human life and the environment. Groundwater lowering is of ten the most efficient way to stabilize large unstable ground masses. Among groundwater lowering measures, drainage tunnels have several advantages, although construction costs may be proportionally high. This paper presents the concepts involved in the design and construction of drainage tunnels. Three case histories, two in Brazil and one in Argelia are presented, including geological background and monitoring results, where large landslides were stabilized using deep drainage through tunneling solutions.