Abstract: The pore water pressure is the basic concept in soil mechanics. It is also the foundation of the principle of effective stress and the consolidation theory of saturated soils. In this paper, the pore water pressure in soils in static groundwater and in steady seepage field is defined as the static pore water pressure. The excess pore water pressure is induced by external action including loading and change of boundary condition in soils, and the change of the excess pore water pressure is always accompanied with that of soil volume. Some examples are also discussed.