The Lonely Guy is a 1984 American romantic comedy film directed by Arthur Hiller and starring Steve Martin. The screenplay is credited to Ed. Weinberger and Stan Daniels (of Taxi) as well as Neil Simon (for "adaptation"), and is based on the 1978 book The Lonely Guy's Book of Life by Bruce Jay Friedman.

Martin portrays a greeting card writer who goes through a period of bad luck with women. In his despair, he writes a book titled A Guide for the Lonely Guy, which changes his life. The film also stars Charles Grodin, Judith Ivey, and Steve Lawrence and features cameo appearances from Merv Griffin, Dr. Joyce Brothers, and Loni Anderson. The theme song, "Love Comes Without Warning," was performed by the band America.