Because of their varying channel styles (braided, meandering, and anastomosing) medieval lowland floodplains in England and Wales provided varying opportunities for defense, settlement, river crossing, and resource exploitation. In turn, these activities altered the character of channels and floodplains, with medieval and later development obscuring the former variety of floodplains themselves. The changing nature of river floodplains is reviewed using archaeological, documentary, and geomorphological evidence. Anastomosing channels and floodplain wetlands have now all but disappeared but were formerly of considerable significance; also discussed are interactions involving flooding, fording, bridging, modifications to channels and their dimensions, and those arising from accelerated soil erosion—most of which peaked in the medieval period when floodplains were significantly transformed. Deliberately or inadvertently, dynamic floodplain landforms were interactively involved with human development during a critical time period in a totality of ways not previously fully identified. © 2010 Wiley Periodicals, Inc.