Emphasis in ground-water development, once directed largely to quantitatively minor (but sociologically vital) service of human and stock needs, is shifting: aquifers are treated as possible regulating reservoirs managed conjunctively with surface water. Too, emphasis on reducing stream pollution is stimulating interest in aquifers as possible waste-storage media. Such management of aquifers requires vast amounts of data plus a much better understanding of aquifer-system behavior than now exists. Implicit in this deficiency of knowledge is a need for much new research, lest aquifers be managed according to ineffective rule-of-thumb standards, or even abandoned as unmanageable. The geohydrologist's task is to define both internal and boundary characteristics of aquifer systems. Stratigraphy is a primary determinant of these characteristics, but stratigraphically minor features may make aquifers transcend stratigraphic boundaries. For example, a structurally insignificant fracture may carry more water than a major fault; a minor stratigraphic discontinuity may be a major hydrologic boundary. Hence, there is a need for ways of defining aquifer boundaries and quantifying aquifer and confining-bed characteristics that are very different from ordinary stratigraphic techniques. Among critical needs are techniques for measuring crossbed permeability; for extrapolating and interpolating point data on direction and magnitude of permeability in defining aquifer geometry; and for accurately measuring geochemical properties of water and aquifer material, and interpreting those measurements in terms of source of water, rate of movement, and waste-sorbing capacities of aquifers and of confining beds--in general, techniques adequate for predicting aquifer response to imposed forces whether static, hydraulic, thermal, or chemical. Only when such predictions can be made routinely can aquifer characteristics be inserted into a master model that incorporates both the hydrologic and the socioeconomic facts necessary to intelligent social actions involving water.