"Jeffty Is Five" is a fantasy short story by American writer Harlan Ellison. It was first published in The Magazine of Fantasy & Science Fiction in 1977, then was included in DAW's The 1978 Annual World's Best SF in 1978 and Ellison's short story collection Shatterday two years later. According to Ellison, it was partially inspired by a fragment of conversation that he mis-heard at a party at the home of actor Walter Koenig: "How is Jeff?" "Jeff is fine. He's always fine," which he perceived as "Jeff is five, he's always five." Additionally, Ellison based the character of Jeffty on Joshua Andrew Koenig, Walter's son.