Floodplains are a distinctive, often highly productive wetland ecosystem that harbors unique combinations of biodiversity and contributes to ecosystem services by virtue of the hydrological connectivity with rivers. This chapter provides an overview of floodplains along large rivers, emphasizing how geomorphology and hydrology interact to determine spatial and temporal variability in flood regimes, which in turn affect ecosystem structure and function. Regulation of rivers by damming and conversion of floodplains to agricultural uses have degraded or destroyed floodplains throughout the world, but relatively natural floodplain systems remain along large rivers in less populated regions, particularly in the Tropics.