The Jiangmen Underground Neutrino Observatory (JUNO) is a medium baseline reactor neutrino experiment under construction at Kaiping, Jiangmen in Southern China. It aims to determine the neutrino mass hierarchy and perform precision measurements of the Pontecorvo–Maki–Nakagawa–Sakata matrix elements. It will build on the mixing parameter results of many previous experiments. The collaboration was formed in July 2014 and construction began January 10, 2015. The schedule aims to begin taking data in 2021. Funding is provided by the Chinese Academy of Sciences, but the collaboration is international.