The literature on evaluation of irrigation planning and investment is more extensive than any other area of economic investigation of irrigation. The broader questions involve trade-offs among different types of investment including the following: government vs. private irrigation projects; wet-season irrigation vs. year-round irrigation; irrigation vs. rainfed production; expansion vs. intensification of irrigation; and large-scale vs. small-scale irrigation. Governments and international lending agencies are continually asking whether irrigation investment should be large-scale or small-scale and whether the emphasis should be on new projects or on rehabilitation including development of drainage and terminal infrastructure. New systems present a sign of progress that has strong political appeal, both internally and externally; and which may have a more general psychological value. Investments to improve irrigation at the farm level have shown a wide range of economic returns. Many countries must make choices as a matter of policy between large- and small-scale irrigation systems and concentrated vs. dispersed systems.