Basin-wide mosaics of synthetic aperture radar (SAR) data, validated with airborne videography, were used to map the extent and distribution of Amazonian wetlands. Cover states consisted of classes determined by vegetation physiognomy (non-vegetated, herbaceous, shrub, woodland, and forest) and by inundation state (flooded or non-flooded). About one-fourth of wetlands are in the Madeira basin. Large wetland features occur in the Marañón (Marañón-Ucayali palm swamps), Negro (Roraima savanna; Negro-Branco interfluvial wetlands), and Madeira (Llanos de Moxos) basins. The mainstem Amazon floodplain, with less than 2% of the total basin area, accounts for about 12% of the basin’s wetlands. Basin-wide, about three-fourths of wetlands are covered by forest, woodland or shrubland. All large watersheds west of the Negro are at least 85% forested. The Madeira basin has the highest percentage of herbaceous wetlands. Numerous remote sensing studies of wetlands using SAR, passive microwave and optical data for selected areas that complement these basin-wide values are summarized.