Estimation of crop water requirements is one of the main components used in irrigation planning, design and operation. Crop water requirements vary during the growing period, mainly due to variation in growth stages of crop and climatic conditions, and related to both cropping technique and irrigation methods. This book describes the various methods used for estimating reference evapo-transpiration (ETo). The daily ETo have been determined for eighteen stations spread across the diverse climatic conditions of Gujarat following FAO Penman-Monteith approach. Step by step procedure has been described to compute each parameter required in determining ETo. The daily, weekly, monthly, seasonal variability have been displayed in graphical form. The procedure to determine the corrected values of crop coefficients (Kcmid and Kcend) for major crops (rice, wheat, maize, pearl millet, chickpea, green gram, soybean, castor, groundnut, mustard and cotton) at different locations have been explained. The crop water requirement (ETc) determined for different crops across the locations using ETo and Kc values are presented and explained. This book describes variability in crop water requirement of different crops over the locations, periods and seasons. The information provided in the book would be useful to planners in managing irrigation scheduling in different parts of India.