This manual contains the engineering tools and concepts that have proven useful in planning, constructing, and maintaining drainage systems for successful long-term irrigation projects. The manual is not a textbook. Mathematical and experimental development of the engineering tools has generally not been included. Indeed, not even all the innovative ways to use the tools are included. The manual provides drainage engineers a ready reference and guide for making accurate estimates of drainage requirements. Design and construction criteria, if followed with reason, will result in reliable drainage systems for irrigated areas. All the methods and techniques covered in the manual have proven to be very satisfactory through observed field conditions on irrigated lands throughout the world. Some methods have a more elegant development and basis in science than others, but all have been designed to solve practical problems in the field.