Jim Jacobs (born 1942) is an American composer, lyricist, and writer for the theatre.

Born in Chicago, Illinois, Jacobs attended Taft High School, during which time he played guitar and sang with a band called DDT & the Dynamiters. In 1963, he became involved with a local theatre group that included Warren Casey. For the next five years he appeared in more than fifty theatrical productions in the Chicago area, working with such people as The Second City founder Paul Sills, while earning a living as an advertising copywriter. He also landed a small role in the 1969 film Medium Cool.

Jacobs' Broadway acting debut was in a 1970 revival of the play No Place to Be Somebody, followed by the national tour. At the same time, he and Casey were collaborating on a play about high school life during the golden age of rock 'n' roll in the 1950s. Entitled Grease, it premiered in 1971 at the Kingston Mines Theater in the Old Town section of Chicago. Producers Ken Waissman and Maxine Fox saw the show and suggested to the playwrights that it might work better as a musical, and told them if the creative partners were willing to rework it and they liked the end result, they would produce it off-Broadway. The team headed to New York City to collaborate on what would become Grease, which opened at the Eden Theatre in downtown Manhattan, moved to Broadway, and earned him a Tony Award nomination for Best Book of a Musical. The show went on to become a West End hit, a hugely successful film (for which he and Warren wrote additional songs), and a staple of regional theatre, summer stock, community theatre, and high school drama groups.

Jacobs served as a judge on the NBC reality series Grease: You're the One that I Want!, designed to cast the lead roles in an August 2007 Broadway revival of Grease via viewer votes.