The physical, chemical, and biological characteristics of soil bodies, interacting with weather, management practices, and chemical and biological processes, influence the movement of gas, water, and solutes in cropland ecosystems. The activities of soil biota, especially through their effects on soil porosity, impact on these properties and processes. This paper reviews methods for measuring flow into and through the soil, with emphasis on the techniques being developed to assess the importance of biological activity on the flow characteristics of soils. The discussion of methods used to characterize gas, water, and solute transport in soils addresses conditions under which their use may or may not be appropriate and the need for further methodology development.