This study summarizes and reviews 70 models and methods used to determine appropriate instream flow requirements or to characterize stream habitat quality. In addition to these reviews, it includes chapters on selecting and transforming input and output variables, choosing model structure, and determining model parameters. The authors conducted sensitivity analyses on several of the models, and they also report on all of the validation studies that they were able to obtain. They conclude that although many approaches to instream flow determination have been tried, none of them have been linked adequately to biological responses: the field is crowded with competing unvalidated methods. The report identifies a number of research activities that would be useful for developing valid, biologically predictive instream flow methodologies. http://www.epri.com