Old One, Old Ones, Great Old One or Great Old Ones may refer to:

• The Great Old Ones, fictional Cthulhu Mythos deities in the works of H. P. Lovecraft
• The Elder Things, fictional Cthulhu Mythos creatures in the works of H. P. Lovecraft
• The Great Old Ones (Call of Cthulhu), an adventure supplement for the Call of Cthulhu role-playing game by Chaosium
• The Old One, a character in The Keys to the Kingdom
• "The Old One", an episode of Playdate
• Old Ones (Palladium Books), a 1984 book written by Kevin Siembieda
• Old Ones (Buffy the Vampire Slayer), fictional demons in Buffy the Vampire Slayer
• Old Ones, mystical beings in The Dark Is Rising Sequence
• Old Ones, an ancient race of advanced, god-like aliens in the Warhammer Fantasy setting
• Old Ones or Elder Bairns, fictional creatures in Blood-C

• Ancient One (disambiguation)
• Elder race, a fictional ancient race of beings