Working with Costa Rica, Papua New Guinea proposed the concept of reducing emissions from deforestation and forest degradation (REDD+) to the United Nations Framework Convention on Climate Change (UNFCCC) in 2005. Ever since, the country has continued to prepare for REDD+ and has worked to establish a National Forest Monitoring System (NFMS). These actions are vital, as accurate information regarding forest status and change is essential for sustainable management of the nation's forest. The Climate Change and Development Authority (CCDA) and the Papua New Guinea Forest Authority (PNGFA) are the core-implementing partners that jointly developed the country’s NFMS, and they receive support from a number of stakeholders and other actors, including FAO. This case study reviews the main objectives of the county's NFMS, highlights key stakeholders and defines successes and challenges of implementation. Ultimately, this case study serves as a reference for other countries implementing NFMS and preparing for REDD+.