This paper reviews the economics literature on foreign aid. Aid supporters tend to emphasize results, while its detractors tend to highlight the incentives it provides (although they may still acknowledge some of aid’s positive results, particularly on public health). Like the modes to deliver it, research on foreign aid has evolved over the years. From the traditional aid-growth regressions research has refocused towards micro issues, including institutional inefficiencies or sector-specific bottlenecks. This tendency is positive, in so far as it can lead to useful policy advice that improves the way aid is given. Great gaps in knowledge remain, though. Notably, the aid market is poorly understood in aspects such as donors’ interaction wit...