In international relations, aid (also known as international aid, overseas aid, foreign aid, economic aid or foreign assistance) is – from the perspective of governments – a voluntary transfer of resources from one country to another.

Aid may serve one or more functions: it may be given as a signal of diplomatic approval, or to strengthen a military ally, to reward a government for behavior desired by the donor, to extend the donor's cultural influence, to provide infrastructure needed by the donor for resource extraction from the recipient country, or to gain other kinds of commercial access. Countries may provide aid for further diplomatic reasons. Humanitarian and altruistic purposes are often reasons for foreign assistance.

Aid may be given by individuals, private organizations, or governments. Standards delimiting exactly the types of transfers considered "aid" vary from country to country. For example, the United States government discontinued the reporting of military aid as part of its foreign aid figures in 1958. The most widely used measure of aid is "Official Development Assistance" (ODA).