The 23rd Annual Meeting of the Greater Mekong Subregion (GMS) Working Group on Environment (WGE AM-23) was held in Siem Reap, Cambodia on 12 July 2017. The meeting reported on achievements and key results of the GMS Core Environment Program (CEP) in 2016 and the CEP work plan for 2017 until the completion of the program in March 2018. The draft CEP Strategic Framework and Action Plan, 2018–2022, (Strategic Framework) and its pipeline of proposed projects were discussed. Progress on preparations for the 5th GMS Environment Ministers’ Meeting (EMM-5), scheduled for February 2018 in Chiang Mai, Thailand, was also discussed.