Official development assistance (ODA) is a category used by the Development Assistance Committee (DAC) of the Organisation for Economic Co-operation and Development (OECD) to measure foreign aid. The DAC first adopted the concept in 1969. It is widely used as an indicator of international aid flow. It refers to material resources given by the governments of richer countries to promote the economic development of poorer countries and the welfare of their people. The donor government agency may disburse such resources to the government of the recipient country or through other organizations. Most ODA is in the form of grants, but some is measured as the concessional value in soft (low-interest) loans.

In 2019, the annual amount of state donor aid counted as ODA was US$168 billion, of which US$152 billion came from DAC donors.

In order to co-ordinate and measure international aid effectively, the DAC needs its members to have agreed clear criteria for what is counted as aid. The precise type of aid to be counted was given the name of official development assistance (ODA) (where "official" indicates that the aid is public and from governments).

The full definition of ODA is:

Flows of official financing administered with the promotion of the economic development and welfare of developing countries as the main objective, and which are concessional in character with a grant element of at least 25 percent (using a fixed 10 percent rate of discount). By convention, ODA flows comprise contributions of donor government agencies, at all levels, to developing countries ("bilateral ODA") and to multilateral institutions. ODA receipts comprise disbursements by bilateral donors and multilateral institutions.

— OECD, Glossary of Statistical Terms

In other words, ODA needs to contain the three elements:

This definition is used to exclude development aid from the two other categories of aid from DAC members: