For the last decades, hydraulic testing and groundwater sampling in high-to-moderate-permeability rocks for the disposal of radioactive waste have become increasingly routine and well documented in literature and textbooks. Applying these methods to low- and very-low-permeability rocks, such as argillaceous rocks, poses new challenges because of their inherent characteristics, and requires modifications in equipment, testing procedures, and interpretation methods. This publication presents the papers of an international workshop discussing the many challenges involved and reviewing the new and innovative techniques being developed throughout the world under the auspices of national programmes for radioactive waste disposal.