AID or Aid may refer to:

• Activation-induced (cytidine) deaminase, an enzyme
• Aid (rapper) (born 1990), stagename of Aida Alonso Iglesias, a Spanish rap singer
• Algebraic Interpretive Dialogue, an implementation of JOSS II for the PDP-10
• Americans for Informed Democracy, an American non-profit organization
• Amputee identity disorder, now more commonly known as Body integrity identity disorder, a controversial psychological and neurological mental disorder
• Artificial Insemination by Donor, a type of human artificial insemination in which donor sperm are provided by an individual other than the recipient's partner
• Association for India's Development, an American/Indian non-profit organization
• Autoimmune disease, a disorder with an overactive immune response of the body
• Automatic Interaction Detection, a precursor to, and component of CHAID
• Aid (Würm), a River in Germany
• The application identifier in the EMV payment card chip standard

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