Despite considerable progress, poverty reduction and sustainable development remain a major challenge for many countries. Aid remains one important component in contributing to progress, but in recent years increasing attention has been paid to some of the challenges for aid effectiveness. Linked to this, there has been growing recognition of the ways that aid can impact on and be affected by accountability, governance and politics in donor and recipient countries. However, a real gap in understanding remains with regard to the relationship between aid effectiveness and accountability, and whether and how the two can reinforce each other. This report, commissioned by World Vision UK, looks at these issues in the case of Uganda and Zambia, using the health sector as a lens.