When HARLIE Was One is a 1972 science fiction novel by American writer David Gerrold.

A revised version, subtitled "Release 2.0", was published in 1988 by Bantam Books.

Central to the story is an artificial intelligence named H.A.R.L.I.E., also referred to by the proper name "HARLIE"—an acronym for Human Analog Replication, Lethetic Intelligence Engine (originally Human Analog Robot Life Input Equivalents).

[2][3] Theodore Sturgeon reported that the novel "carries a good freight of social and psychological insight".

[4] The HARLIE intelligence engine appears in a number of Gerrold's other works: