We compare the effectiveness of conditional budget support and project aid in poverty reduction programs, in a model in which altruistic donors have preferences not perfectly aligned with those of recipient governments. We Þnd that project aid is a better (worse) instrument to alleviate poverty than budget conditionality when: (i) aid programs are relatively large (small) with respect to the recipient's country resources; and (ii) recipient governments are relatively less (more) socially committed. In addition, we show that when donors cannot observe the recipient's type, they may impose a higher level of conditionality on budget support programs as a device to separate socially committed governments form uncommitted ones. JEL ClassiÞcation Numbers: D8, I3.