The Global Climate Observing System (GCOS) reference Upper-Air Network (GRUAN) community has progressed in achieving the goal of constructing an observing network that, ultimately, will meet the challenges of climate science in the twenty-first century. To maximize the impact of GRUAN activities, GRUAN scientists participate in coordinated international programs and collaborate with colleagues internationally. The tiered 'system of systems' architecture envisioned for in situ upper-air soundings identified GRUAN as the reference tier, the GCOS Upper-Air Network (GUAN) as a baseline capability, and the remainder of the radiosonde network providing regional detail. In 2012, GRUAN partnered with the Network for the Detection of Atmospheric Composition Change to realize benefits of sustained cooperation and joint development of data streams and analysis capabilities. To meet the clearly articulated observational needs of organizations such as the Intergovernmental Panel on Climate Change, and to maintain existing momentum, GRUAN needs the commitment of national meteorological services in establishing new sites in regions currently not represented in the network, in demonstrating the utility of GRUAN reference data by the climate research community, and in committing long-term support from national funding agencies.