This Project Briefing, the third of three, draws on ODI research in Uganda and Zambia on aid accountability in the health sector, to focus on donors. The health sector is seen as a ‘tracer sector’ for accountability in aid, in part because of the high levels of support it receives. The ODI research, on behalf of World Vision UK, finds that the failure of many donors to fulfil their commitments to mutual accountability in the health sector has contributed to one-way accountability – to donors rather than to citizens – in Uganda and Zambia. It suggests that donors need greater interaction with domestic processes and accountability mechanisms.