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"Because programs that have been shown to be successful can be replicated in other countries, while unsuccessful programs can be abandoned, impact evaluations are international public goods: international agencies should therefore have a key role in promoting and financing them. In doing so, they would achieve three important objectives: improve the rates of return on the programs they support; improve the rates of return on the programs other policy makers support, by providing evidence on the basis of which programs can be selected; build long-term support for international aid and development, by making it possible to credibly signal what programs work and what programs do not work. The paper argues there is considerable scope to expand the use of randomized evaluations. For a broad class of development programs (although not all), randomized evaluation can be used to overcome the problems often encountered when using evaluation practices. First, it discusses the methodology of randomized evaluation through several concrete examples, mostly drawn from India. It then discusses the potential of randomized evaluation as a basis for upscaling projects. Finally, it discusses current practices and the role international agencies can play in promoting and financing rigorous evaluations."