Irrigation is a required management practice in pistachio nut production for higher quality and quantity. A proper irrigation management technique that maintains an optimum soil moisture and environment in the root zone increases yield of the pistachio nut tree. Since pistachio tree on the Pistacia vera rootstock does not tolerate excess water in the root zone, over-irrigation must be avoided. In the determination of water requirement of pistachio tree, pan evaporation is commonly used due to its simplicity. However, development and use of a stochastic evapotranspiration model involves solar radiation, vapour pressure deficit and leaf area index and can be a more accurate solution in the irrigation of the pistachio orchard. General principles of irrigation and irrigation management of pistachio nut trees were given in this study.