This Project Briefing, the second of three, draws on ODI research in Uganda and Zambia on aid and accountability in the health sector. The research, carried out on behalf of World Vision UK suggests that there are limits to the impact of donor aid on strengthening accountability in recipient countries, which is complex, dynamic and largely driven by internal processes. Some forms of donor aid can, however, make a difference, either by ‘doing no harm’ or by strengthening domestic accountability systems. The evidence from Uganda and Zambia reveals too little mutual accountability between governments and donors.