The question of how to deal with fractured rock domains has always been on the agenda of geohydrologists. Are Darcy's law and the theory of flow through porous media applicable to fractured rock aquifiers, at least when the flow is assumed to be in the laminar flow range? Is the continuum approach applicable? This subject has also been investigated by reservoir engineers because many important petroleum reservoirs are in fractured rock formations. Of special interest are reservoirs composed of fractured porous rocks, in which the blocks surrounded by the network of fractures are porous. The permeability of such blocks is often rather low, but the porosity, and hence the storage capacity for fluids, is very high. This "double porosity" model for fractured porous rock domains was first introduced in the field of reservoir engineering.;In the past two or three decades, fractured rock domains have received increasing attention not only in reservoir engineering and hydrology, but also in connection with geological isolation of radioactive waste. Locations in both the saturated and unsaturated zones have been under consideration because such repositories are sources of heat and potential