ICOLD Bulletin 150, Cutoffs for Dams, discusses foundation treatment methods using cutoff-type barriers. High emphasis is given to alluvial deposits throughout this document; however, different materials may require cutoff. The construction of cutoffs has made significant advances mainly through the development of more powerful machinery for drilling and excavation, but also through the introduction of new concepts and techniques, such as jet grouting and deep soil mixing. The following types of cutoffs are presented in this Bulletin: - Diaphragm walls - Vib walls - Pile walls - Superimposed concreted galleries - Jet grouting - Deep mixing These methods are described, and the practical application of each method is illustrated by selected case histories. These case histories also demonstrate how certain difficulties specific to a particular dam site have been dealt with. The performance of cutoffs should be monitored so that their efficiency in reducing flow and piezometric head can be evaluated. Piezometers installed in the foundation upstream and downstream of the cutoff are needed to meet this objective.