The Southeast Asian uplands provide livelihood opportunities for more than 100 million people. Many of these are poor smallholder farmers who are economically, socially and politically marginalized, suffer from tenure insecurity and have few options other than drawing on the uplands' natural resources to sustain their living. Forest conversion, inappropriate land use practices and timber logging by a variety of actors have caused widespread resource degradation problems, such as deforestation, decline of biodiversity, erosion, water pollution, and flooding of downstream areas (often referred to as 'negative externalities' in the economic literature). On the other hand, sustainable resource management practices, such as community forestry, paddy rice terracing, and in-situ conservation of plant and animal genetic resources through local ecological knowledge, have generated a range of valuable environmental services (or 'positive externalities') that have remained often unnoticed and largely unrewarded by downstream dwellers, urban citizens, national governments, and international donors. These ecological services can be classified into local or regional commons, such as erosion and flood control, seasonal stream flow regulation, and clean drinking water, and global commons, such as carbon sequestration and biodiversity.