This paper provides a critical assessment of the performance of EIA as a planning tool in Tanzania. The research represents the first attempt to review EIA in a developing country context, based on detailed field assessment, interviews and literature reviews. The findings suggest that, despite substantial investment in EIA in Tanzania by government, private sector and donor agencies alike, EIA has largely failed to influence planning and policy. This challenges widely-held assumptions of EIA effectiveness. The report outlines a number of policy options for making EIA a more effective policy instrument. The study was undertaken in partnership with the Institute of Resource Assessment (IRA) at the University of Dar es Salaam, Tanzania.