In both natural and agricultural systems, soil fauna can be an important regulator of decomposition, nutrient cycling, soil organic matter dynamics and pathways of water movement as a consequence of their feeding and burrowing activities. In the tropics, the effects of earthworms and termites, also referred to as 'soil ecosystem engineers', are particularly pronounced because their activities influence the distribution of organic matter in the soil profile and the physical structure of soil. These organisms therefore represent a resource that should be properly documented and managed, as reflected in the approaches and findings of the six year (1990-1996) Macrofauna programme, funded by the European Union and involving researchers from eight different institutions, working in twelve tropical countries of America, Africa and India. In seeking to evaluate the potential represented by earthworms in humid tropical agroecosystems, a world-wide biogeographical survey of tropical earthworms first sought to identify species with some potential to resist disturbances linked to agricultural practices and to assess tolerance to a range of environmental parameters. One product is a database of 457 earthworm species from 28 countries with detailed geographical, environmental and socio-economic data of the sites of collection. Sampling of macro-invertebrate communities in 73 sites has highlighted the relative importance of earthworms in soil communities and the impact of different types of land use on these communities. Selected earthworm species have been further studied for their biology, demographic characteristics and effects on plant growth, soil organic matter dynamics and soil structure. This work has provided a basis for specific technologies based on the utilization of soil-dwelling earthworms and low-quality organic residues for improving agricultural performance.