Scientific visualization is increasingly being applied in many large-scale groundwater modeling efforts as an effective means of presentation and interpretation of model results. An interpolation or statistical approach is applied to develop three-dimensional spatial distributions of geologic, hydraulic, and chemical data from a model or field measurements. The distributions become the basis for evaluating spatial variation of data. The evaluation is accomplished by displaying data in the form of isosurfaces of values of data or as contours of data on a surface or plane. This approach of analyzing data is known as data visualization. In addition to data visualization, some of the problems encountered in groundwater hydrology require visualization of groundwater flow and transport processes. Display of hydraulic and chemical data for analysis of groundwater flow and transport processes is herein referred to as process visualization. In both data and process visualization, hydraulic and chemical data are displayed as color contours or isolines on surfaces. However, in data visualization the surface on which data are displayed may be oriented in any direction, whereas in process visualization the surfaces need to be tangential or orthogonal to the direction of groundwater flow. In three-dimensional groundwater flow, stream surfaces and pseudopotential surfaces are tangential and orthogonal, respectively, to the direction of groundwater flow. Therefore stream and pseudopotential surfaces provide natural platforms on which to visualize groundwater flow and transport processes. To demonstrate application of stream and pseudopotential surfaces in process visualization, the three-dimensional groundwater flow beneath the Borden Landfill is considered. ¿ American Geophysical Union 1996