The purpose of dams is to retain water or, in the case of tailings dams, to retain saturated materials. In most cases, the body of a well-performing dam can be considered impervious; however, seepage through the foundation depends on the geological conditions and is often excessive. This seepage is usually controlled by grout curtains, cutoffs, or a combination of both. Illustrated by recent case studies, this paper will present and discuss cutoffs and their recent technological developments: different construction techniques and materials constituting the cutoffs; excavation equipment; and the monitoring technologies used during and after excavation to ensure the quality of the final product. The challenges of new-build construction and of dam repair will also be addressed.