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certain desired restorative actions (e.g., eradication of exotic species, reintroduction of extinct native species), and philosophical differences among stake- holders and disagreements over who should bear the social and economic costs of restoration. Resolving resource- management issues across entire river basins and resolving conflicting interests among stakehold- ers requires degrees of coordination and cooperation rarely achieved in human society [Naiman, 1992]. However, as the public increasingly recognizes the link between ecological integrity and ecosystem goods or services such as clean water or productive fisheries, shifts in values may induce people to rethink assump- tions about what is sociopolitically acceptable in res- toration scenarios. For example, should reduced flood flows downstream from a dam constrain restoration efforts, or should restoration include greater flood - flow releases from the dam? Many factors assumed to be constraints twenty years ago are being re- examined as opportunities to restore rivers today. Rather than a dichotomy between pro - development and pro- environ- ment, many scientists and practitioners are realizing that there is a middle ground in which some functions can be restored without great cost to water users. River restoration can also be advanced by treating restoration projects as experiments that can teach us about ecosystem operation. Most restoration projects have been implemented without the study design, baseline data, and post - project appraisal needed to learn from them [Downs and Kondolf, 2002; Bern- hardt et al., 2005]. Much of the published literature, which forms the basis of our ecological understand- ing, describes research conducted at space -time scales much smaller than those appropriate for restoration. Furthermore, many restorative actions are applied at scales too small to produce the intended effects on bi- otic populations and assemblages [Pretty et al., 2003]. A major limitation in advancing scientific knowledge to guide predictive restoration is the lack of opportuni- ties to conduct large -scale experiments, where whole system responses can be evaluated at scales that match management actions. For example, restoration of flow regimes below existing water control structures pres- ents tremendous opportunities to learn about system - specific responses that can guide future restoration ac- tions [Poll et al., 2003]. Experimental flood releases such as those on the Colorado River in Grand Canyon [Collier et al., 19971 provide opportunities to pose and test hypotheses regarding the ecosystem effects of these floods. Despite the lack of standard experi- mental features such as randomization of controls and treatments, or replication, the flood releases create quasi- experiments that provide important knowledge about river response to restoration efforts [Block et al., 2001]. Viewing restoration projects as experiments affords a framework for engaging scientific involvement early in the process and strengthens the rationale for monitoring the results of the restoration action. Adaptive management coupled with effective moni- toring facilitates learning from experience [Walters, 1997; Rogers, 2003], and has been repeatedly identi- fied as a critical and missing component of existing river management programs such as that on the Platte River [National Research Council, 2005]. We cur- rently have far too few experiments at appropriate scales that are conducted adaptively and thus we have not yet developed scientific guidelines for how best to restore adaptively or over what timescale adaptive management should be applied. In summary, recent overviews of the state of river restoration in the U.S. have highlighted existing prob- lems and suggested directions for improvement. We suggest that river restoration can be most effectively advanced with increasing emphasis on (i) implement- ing restoration within a clearly articulated scientific conceptual framework and a watershed context, (ii) restoring process rather than form, and (iii) monitor- ing and learning from ongoing restoration efforts. It is not unreasonable for society to expect a return on their investment in river restoration. References Cited Angermeier, P.L (1997), Conceptual roles ofbiologi- cal integrity and diversity, in Watershed restora- tion: principles and practices, edited by J.E. Wil- liams, C.A. Wood and M.P. Dombeck, pp. 49 -65, American Fisheries Society, Bethesda, MD. Baron, J.S., N.L. Poff, P.L. Angermeier, C.N. Dahm, P.H. Gleick, N.G. Hairston, R.B. Jackson, C.A. Johnston, B.G. Richter, and A.D. Steinman (2002), Meeting ecological and societal needs for freshwater, Ecological Applications, 12, 1247- 1260. Bernhardt, E.S., M.A. Palmer, J.D. Allan, and the National River Restoration Science Synthesis Working Group (2005), Restoration of U.S. riv- ers: a national synthesis, Science, 308. Block, W.M., A.B. Franklin, J.P. Ward, J.L. Ganey,