The mountains in northeastern Thailand cover an area of about 25,000 km², which is about 15% of the region's land surface. Although agriculture is the most important economic activity in the mountains, there has been little previous research on it. This study presents a general description of mountain agriculture in northeastern Thailand, which is shown to be quite different from the better-known agriculture in Thailand's northern mountains. The northeastern mountains are diverse in environment, culture, and land use. Mountain agriculture is also diverse at the crop level. Field crops remain the main source of income, but in recent years, rubber has become increasingly important in some areas. Specialty crops (eg grapes, strawberries, exotic flowers, and temperate vegetables) generate high income and serve as a magnet for tourism, but they are grown in only small areas in a few favored locations. Poor-quality soil, seasonality and variability of rainfall, scarcity of surface water, broken terrain and steep slopes, insufficient supply of land, land tenure insecurity, limited possibilities for mechanization, high cost of transportation, and competition with foreign imports are the main constraints on development. However, promotion of specialty crops and agritourism offer some potential for mountain agricultural development in northeastern Thailand.