The UCAR/CU CYGNSS inundation maps provide estimates of fractional surface water extent derived from NASA’s Cyclone Global Navigation Satellite System (CYGNSS), a constellation of eight microsatellites launched in December 2016. Each satellite carries a Global Navigation Satellite System Reflectometry (GNSS-R) receiver that measures L-band GPS signals reflected from the Earth’s surface. The inundation fraction is retrieved by assuming that the observed reflectivity within each 3 km grid cell represents a weighted average of the reflectivities of its inundated and non-inundated fractions, weighted by their respective areal proportions. The temporal range of UCAR/CU CYGNSS v3.2 data is 1 August 2018 to 31 December 2025, and each corresponding daily file contains five distinct variables: (i) 1-day inundation observations, containing retrievals for valid, directly observed grid cells (no spatio-temporal inter-polation); (ii) 3-day interpolated inundation, obtained by interpolating three-day observation aggregates; (iii) interpolation flags, distinguishing directly observed and interpolated grid cells in the three-day product; (iv) 1-day inundation anomalies, expressing departures of daily observations from the seasonal cycle; and (v) 3-day interpolated inundation anomalies ex pressing departures of the three-day interpolated values from the seasonal cycle. The dataset has a spatial resolution of 3 km and geographic coverage extending approximately from 38° N to 38° S, consistent with the CYGNSS orbital inclination.