The Water Vapor Sensing System, second generation, WVSS-II, enables high quality Upper Air Water Vapor Measurement from commercial and research aircraft platforms. WVSS-II is certified for use in commercial aviation on multiple aircraft types and by multiple civil aviation authorities, and is easily installed for research applications. WVSS-II is used globally by National Meteorological and Hydrological Services and their partner airlines as a component of the WMO Aircraft Based Observations Programme (ABOP). Approximately 150 commercial aircraft have been equipped with WVSS-II to report real-time data into the global ABOP systems. WVSS-II is also used in many research projects for atmospheric sciences and aviation at Government, Corporate, and University research facilities. Independently evaluated, verified, and proven over years of operational use, WVSS-II is the most sustainable solution for high quality Water Vapor Measurements.