A new model explicitly incorporates the possibility of rapid response, across signifi cant distance, to substan al water input. It is useful for unsaturated fl ow processes that are not inherently diff usive, or that do not progress through a series of equilibrium states. The term source-responsive is used to mean that fl ow responds sensi vely to changing condi ons at the source of water input (e.g., rainfall, irriga on, or ponded infi ltra on). The domain of preferen al fl ow can be conceptualized as laminar fl ow in free-surface fi lms along the walls of pores. These fi lms may be considered to have uniform thickness, as suggested by fi eld evidence that preferen al fl ow moves at an approximately uniform rate when generated by a con nuous and ample water supply. An eff ec ve facial area per unit volume quan ta vely characterizes the medium with respect to sourceresponsive fl ow. A fl ow-intensity factor dependent on condi ons within the medium represents the amount of source-responsive fl ow at a given me and posi on. Laminar fl ow theory provides rela ons for the velocity and thickness of fl owing source-responsive fi lms. Combina on with the Darcy-Buckingham law and the con nuity equa on leads to expressions for both fl uxes and dynamic water contents. Where preferen al fl ow is some mes or always signifi cant, the interac ve combina on of source-responsive and diff use fl ow has the poten al to improve predic on of unsaturated-zone fl uxes in response to hydraulic inputs and the evolving distribu on of soil moisture. Examples for which this approach is effi cient and physically plausible include (i) rainstorm-generated rapid fl uctua ons of a deep water table and (ii) space-and me-dependent soil water content response to infi ltra on in a macroporous soil.Dual-domain models are oft en used to quantify fl uxes of water and other substances through unsaturated zone materials with complex structure. Typically, the separate domains correspond to preferential and nonpreferential (diff use) fl ow. Most commonly the nonpreferential domain is formulated according to the traditional Darcy-Buckingham law for fl uxes and Richards' (1931) equation for transient water contents. Th e preferential domain may use Richards' equation also (e.g., Gerke and van Genuchten, 1993) or kinematic waves (e.g., Larsbo and Jarvis, 2003) or other approaches. All options neglect or simplify some of the processes and geometries of preferential fl ow. Th ere is the additional major problem that many processes critical to preferential fl ow are signifi cantly diff erent from those of nonpreferential fl ow and are poorly understood. Capillarity, for example, is a dominant infl uence in diff use unsaturated fl ow but probably not in many types of preferential fl ow. Other needs for preferential fl ow models are to maximize the use of commonly available information (e.g., visually observable characteristics of rocks, soils, and weather) and reduce the need for data that are rarely known (e.g., unsaturated hydraulic conductivity as a spatially...