The Sumatran orang-utan is in dramatic decline, including the population in its main stronghold, the Leuser Ecosystem, in Sumatra, Indonesia (C. P. van Schaik et al. (2001) Oryx 35, 14–25). The major threats to the survival of Sumatran orang-utans are identified as habitat loss (mainly from conversion to oil palm plantations), habitat degradation and habitat fragmentation. The immediate causes of this are identified as weak compliance with regulations and laws; weak law enforcement and the weak legal environment. Corruption is identified as the ultimate causal factor underlying these three immediate causal factors, along with a frontier mentality and bureaucratic constraints. Together, they have resulted in the destruction of prime orang-utan habitat. Several political actions are recommended to improve the effectiveness of habitat conservation for the orang-utan and several technical challenges are to be overcome once the policy context is right. The most crucial problem to solve is the lack of regular funds for enforcement operations and establishing a new system of enforcement that is effective. In addition, the Gunung Leuser National Park needs to be redesigned by enlarging it to cover all high biodiversity areas within the Leuser Ecosystem. Moreover, habitat corridors between important forest tracts need to be re-established.