In Tanzania, land rehabilitation seems promising for repairing damaged ecosystems and provide sustainable supply of forest and food products, thus securing vital environmental services including increased carbon sequestration for global climate change mitigation. Comprehensive estimates of how large areas Tanzania has of degraded land are however lacking. This study aimed to (i) assess the area of degraded land potentially available for rehabilitation in various regions of the country, and (ii) give a review of main experiences and economic results gained in previous land rehabilitation studies in the country. Based on new data from the National Forest Resource Monitoring and Assessment of Tanzania we found that about 49 % (43.3 mill ha) of the total land area in Mainland Tanzania is under either light (43 %, 37.7 mill ha), moderate (5 %, 4.4 mill ha) or heavy (1.3 %, 1.2 mill ha) erosion. These areas are substantial, and imply large opportunities for land rehabilitation. None economic studies were found which have calculated benefits and costs of land rehabilitation in Tanzania. Such studies are urgently needed in order to identify and prioritize among the most promising rehabilitation activities