A model for determining the potential and actual evapotranspiration from agricultural crops is presented. The model requires only a limited number of meteorological variables, i.e. global radiation, air temperature and precipitation. The vegetation is characterized by the crop surface area and the efficient root depth. The soil is characterized by the root zone capacity. The model simulates evaporation of intercepted water, evaporation from the soil surface and transpiration from plants. The evapotranspiration pressure (potential evapotranspiration) is divided between crop and soil by use of Beer's law.