Degraded soils are abundant all over the world; the agricultural use of these soils is very difficult or unprofitable. Forestry is a possibility of use and rehabilitation of degraded soils, useful for stabilisation and protection of unstable sites like river and seashores, sand dunes and steep slopes. Nitrogen fixing trees, either legume or actinorrhizal trees, form a symbiotic association with nitrogen fixing soil microorganisms of the genus Rhizobium or Frankia respectively, and also with mycorhizal fungi. These associations allow the fixation of atmospheric nitrogen and the improvement of the assimilation of soil nutrients. In disturbed lands, nitrogen fixing trees can grow better than non-fixing trees or than nitrogen fixing herbaceous plants. Within N2 fixing trees there are species that are tolerant to different constrains like salinity, acidity, heavy metals, drought, fire, invasive weeds, nutrient deficiency, waterlogging, compactation and crusting. These trees are able to recycle big amounts of organic matter and nutrients through litter decomposition, and though other management practices should be also considered, they are an appreciated alternative for rehabilitation of marginal soils. In this work more than 100 tree species are reported and analysed for rehabilitation purpose in different kinds of degraded lands, and under different geographic situations.