River and stream restoration projects are increasingly numerous but rarely subjected to systematic post-project evaluation. The few such evaluation studies conducted have indicated a high percentage of failures. Thus, post-project evaluation (and dissemination of results) is essential if the field of river restoration is to advance. Effective evaluation of project success should include: (1) Clear objectives, essential to identity potential incompatibilities among project objectives and to provide a framework for design of project evaluation. (2) Baseline data, needed as an objective basis for evaluating change caused by the project and encompassing as long a pre-project period as possible (including a detailed historical study). (3) Good study design, to demonstrate the effects of restoration projects in the complex riverine environment. (4) Commitment to the long term, to detect effects evident only years following project completion; in general, monitoring should continue for at least a decade, with surveys conducted after each flood above a predetermined threshold. (5) Willingness to acknowledge failures, or rather to recognize that each restoration project constitutes an experiment, so that a failure can be just as valuable to the science as a success, provided we can learn from it (which requires objective, robust post-project evaluation).