Granier sap flow system is one of the most commonly used techniques for measurements of whole-tree water use in ecophysiological and forest hydrological studies. However, in the literature there is not one paper that exclusively reviews the Granier method. In this paper, we recapitulate the theoretical basis of the Granier sap flow system and review recent developments in calibration and modification of the sensor probes. Practical issues, such as the determination of the non-flow signal values, natural thermal gradient, wounding effect, reversed sap flow pattern and extrapolation of individual measurement of sap flux density to whole-tree sap flow, are discussed in detail. In the perspectives, new approaches are put forward to use the strong coupling between photosynthesis and transpiration or canopy conductance, via the measurement of 13C discrimination, to estimate whole-canopy carbon assimilation.