Abstract Tree crops are representing one of most widespread agricultural systems in Mediterranean regions, thus contributing in a substantial way to the economy and productivity of primary sectors of the countries interested. Besides the aspects concerning their economical relevance, tree crops like vineyards, olive and orange orchards are also typical elements of the Mediterranean landscape, and their ecological role has been recently revitalised in consideration of their function as carbon sinks for the Kyoto agreement. The environmental and economical sustainability of these agricultural systems in arid and semi-arid zones has to cope with the availability and management of water resources for irrigation. During recent years there has been a substantial progress in understanding the evolution of evapotranspiration processes in cropping systems, and detailed models and measurement techniques have been set-up for describing the mass and energy exchanges in the soil-plant- atmosphere continuum. However, due to the complexity of rooting systems and aerial parts further steps are needed for a full comprehension of hydrological processes in tree crop systems, with special regard to water stress conditions. Within the research project P.R.I.N. 2008 “Assessment of mass and energy fluxes for the irrigation management of Mediterranean tree crops” different techniques for measuring evapotranspiration fluxes in tree crops will be developed and tested, from innovative methodologies based on remote sensing observations to in-situ observations (xylem-flow measurements and micro-meteorology). These data-sets have be interpreted by means of physical approaches, with a modelling perspective of the observed processes.