This paper studies interactions between aid and three other major North-South flows : international trade, FDI and migrations. It mainly focuses on the question of whether aid is allocated to countries that are benefiting from the other flows considered here or the reverse. It appears that aid allocation is increasingly compensatory, while its relative weight among other flows, and hence its compensatory power, has decreased over the past three decades. This paper also addresses whether policies carried out in the other dimensions affect the efficiency of a dollar of aid in terms of the poverty reduction. Nevertheless, it appears that the empirical identification of positive complementarities between aid and other policies is particularly difficult to reach.