Forest transpiration models have been developed in dierent disciplines such as plant physiology, ecology, meteorology, hydrology and soil science. In the present study, three dierent types of model perspectives for transpiration control are used: leaf cooling, CO 2 assimilation and the combined energy and water balance. All three process-orientated models are calibrated on measurements in a Douglas ยฎr stand in the Netherlands. The performances of these models are equally good, although they have dierent complexities, dierent numbers of calibration parameters (ranging from 1 to 6) and the models are calibrated on dierent measurements (eddy correlation at canopy level or CO 2 measurements at leaf level). The resemblance of the model results is caused by the calibration procedure and by the high impact of radiation in all three cases. Signiยฎcant discrepancies become apparent when dierences between model responses are examined and when speciยฎc (short) periods are selected when input variables are uncoupled. The main dierences between the models are caused by another formulation of leaf area index and vapour pressure deยฎcit (VPD). Considerable dierences in simulated transpiration occur in the afternoon as a result of the diurnal hysteresis between VPD and radiation.