The book includes an analysis of the assessed measurement methods of evapotranspiration. It includes the related operations to the optimization of water usage in the field of agriculture and to the study of ecosystems. Also, various measuring methods are discussed with comprehensive explanations and examples. Some of them are methods at the leaf, agro-ecosystem and plant levels. For optimized water usage in agricultural field, definite measurements on transpiration requirements of crops and various cultivars, as well as conclusions of various irrigation methods and experiments in semi-arid areas for open field, greenhouse and potted grown plants are discussed in the book. Apart from this, some other topics discussed within the book are the features of ET of crops in saline surroundings, effects of ET on groundwater quality in xeric surroundings and the application of ET to climatic classification. The book presents an overview for both researchers and students who wish to know more about these subjects.