The Ballantine Adult Fantasy series was an imprint of Ballantine Books. Conceived by Betty and Ian Ballantine, and edited by Lin Carter, the series was launched in 1969 primarily to publish (in cheap paperback form) reissues of works of fantasy literature which were out of print or not easily available in the United States. It included works by authors such as James Branch Cabell, Lord Dunsany, William Morris, George MacDonald, Clarke Ashton Smith, Hope Mirrlees and Evangeline Williams. The series also included a number of short fiction collections and anthologies edited with notes by Lin Carter, together with a limited number of new fantasy novels by writers such as Katherine Kurtz and Joy Chant.

Ballantine Adult Fantasy was probably not a significant money-maker, so the series was cancelled when the Betty and Ian left Ballantine Books in 1974 after its acquisition by Random House in 1973. A total of 65 volumes were published, each with an introduction by Lin Carter, with a further two volumes issued subsequently which are closely associated to the series.