Mail art is art which uses the postal system as a medium. The term mail art can refer to an individual message, the medium through which it is sent, or an artistic genre. Mail art is also known as postal art and is sometimes referred to as Correspondence/Mail Art (CMA).

Mail artists typically exchange ephemera in the form of illustrated letters, zines, rubberstamped, decorated or illustrated envelopes, artist trading cards, postcards, artistamps, faux postage, mail-interviews, naked mail, friendship books, decos, and three-dimensional objects.

An amorphous international mail art network, involving thousands of participants in over fifty countries, evolved between the 1950s and the 1990s. It was influenced by other movements, including Dada and Fluxus.

One theme in mail art is that of commerce-free exchange; early mail art was, in part, a snub of gallery art, juried shows, and exclusivity in art. A saying in the mail art movement is "senders receive", meaning that one must not expect mail art to be sent to oneself unless one is also actively participating in the movement.