This introductory paper presents 20 river restoration cases throughout Europe that were investigated in the EU-funded research project REFORM. In the following, this special issue provides seven specific papers that highlight and discuss the effects of restoration on the investigated river–floodplain systems. Additionally, restoration success was estimated from a socio-economic perspective. 

The first part of this paper presents the overall study concept and the general sampling design of the field investigations. Each study site was examined with the same array of methods, covering habitat composition in the river and its floodplain, three aquatic and two floodplain-related organism groups, as well as food web composition and “aquatic terrestrial” interactions as reflected by stable isotopes. An overview of the rivers and the study sites summarizes main attributes of all investigated sites, with emphasis on the large-scale restoration projects. Some of the projects represent the “state of the art” restoration approaches for two major European river types: gravel-bed mountain rivers and sand-bed lowland rivers. Concluding, restoration efforts had positive effects even in the small restoration projects investigated but did not increase with project size. No “single best” measure could be identified, but river widening generally had a larger effect compared to other restoration measures.