Erosion of biodiversity is of global concern. Habitat destruction is the main cause. Many governments have established national park systems to try to protect habitat. National parks have traditionally excluded human settlements and extractive uses, often creating problems for local communities. This has resulted in support for human occupancy of parks, particularly by indigenous peoples. However, indigenous peoples can also have a significant impact on local ecosystems. Thus, a more refined management response is called for, based on assessment of ecosystem impacts and sensitive to local cultural characteristics. A first step is to assess the nature of the interaction between the local peoples and the park. This approach is taken with reference to Doi Inthanon National Park in Northern Thailand. Different ethnic groups have different impacts and therefore warrant different management responses. Some 40% of the park area has been encroached upon. The situation is further complicated because of a development program that has goals that are in conflict with those of the park. Data on use of park resources by local populations reveals an inverse relationship between use and distance from the park. Possible management strategies are suggested.