Following a long history of floodplain degradation, directly or indirectly as a result of river regulation, international attention is turning to the restoration of these ecologically important ecotones. One immediate problem is to assess the ecological value of different floodplain habitats. With reference to two floodplain sectors—one non-regulated and one regulated—on the River Trent, U.K., this paper characterizes the dominant floodplain units using two families of beetles (Coleoptera: Carabidae and Staphylinidae). Five dominant habitat units, riparian, wetland, woodland, pasture, and arable, are clearly differentiated by both families using ordination analyses. Although the faunal assemblages of specific units within the two sectors have many similarities, the units within the regulated sector are more clearly differentiated, having larger assemblages of ‘describer' species. It is suggested that the enhanced environmental gradients between units within this sector may be responsible for stronger faunal contrasts.