: It is estimated that the world population will be 9.6 billion by 2050. In order to meet the food needs of the growing population, it is necessary to increase the yield obtained from existing agricultural land. As the greenhouse provides a more controlled environment, the yield taken from the unit area is higher than the field conditions. For this reason, the greenhouse cultivation has been increased in year by year. Irrigation is one of the major cultural applications for increasing yield from the unit area. It is important that crop water requirement should be determined correctly for proper irrigation scheduling in greenhouse. The use of equations based on climate to determine evapotranspiration has been increased in recent years. In this study, estimation performances of evapotranspiration equations based on the reference crop (Penman, Hargreaves, FAO-24-Radiation, Priestley-Taylor, FAO-Penman Monteith, FAO24-Pan Evaporation) and main crop (Stanghellini, Fynn, Takakura, Simplified Model) developed from the past to the present day were reviewed. It is concluded that there is no standard equation under greenhouse conditions to determine evapotranspiration of a specific crop. The reason for this is that greenhouse climate changes depending on greenhouse type, location, direction, cover material, greenhouse volume, ventilation mechanism, usage of thermal curtain and shadow powder and even cultural applications such as hanging. However, it is possible to develop new equation or calibrate existing equations for each different greenhouse in the same region. Therefore, it is suggested that evapotranspiration equations to be used should be selected depending on the type of greenhouses commonly used in the region and, if necessary, modified according to these conditions.