Acacia mangium, a N2-fixing tree legume, has become a major plantation tree species in the tropical humid and sub-humid zones. In addition to being a major pulp-wood producer, the tree has a good potential to restore soil fertility as a fallow species in agroforestry systems, and as a fuel species. In this paper, we report an overview of the results from several rhizobium inoculation field trials in different edaphic and ecological conditions, conducted by the CIRAD-Forêt (The Forest Program of Centre de Coopération Internationale en Recherche Agronomique pour le Développement) in partnership with national research organizations of various countries of the humid and sub-humid lowlands of West Africa and Cook Islands.Rhizobium inoculation had a positive effect on tree growth up to 39 months after tree planting.