The inundation extent is derived using brightness temperature data acquired by the L-band Soil Moisture Active Passive (SMAP) satellite, to support boreal carbon studies. Exploiting the L-band capabilities to penetrate clouds and vegetation and SMAP's 3-day revisit, the product may complement high-spatial resolution optical products in the high latitudes. The quality of the inundation extent is assessed by comparing with the following data sets: 3-m resolution maps derived using Radarsat synthetic aperture radar (SAR) data in northern Canada and multi-sensor climatology over Siberia. Initial results show encouraging comparisons. SMAP describes the seasonality of inundation more realistically compared with the climatology.