The Integrated Hydrologic Model (IHM) integrates the significant surface and subsurface hydrologic processes for the land based portion of the hydrologic cycle into a single software package. Through the coupling of surface water and ground water process models and the explicit representation of the vadose zone, IHM provides a state-of-the-art public domain windows-based capability to simulate the interaction between surface water and ground water. IHM uses physically-based delineations of land forms into land segments. Each land segment represents a homogeneous hydrologic response unit (HRU) within a drainage basin. A unique land segment is created by intersecting the drainage basins, land use, and soils coverage. IHM parameters are directly derived from land cover and soil data. This paper focuses on evapotranspiration processes as implemented in IHM and explores the behavior of simulated ET rates and their relationships to the ET-controlling parameters.