Film rights were bought to the novel in 1964 by Herbert Swope.
Harriet the Spy was made into a 1996 film of the same name. It starred Michelle Trachtenberg and was the first film to be produced by Nickelodeon's feature film division.
In September 2004, Mainframe Entertainment announced that Protocol Entertainment will produce a new Harriet the Spy live-action television series, consisting of at least 22 half-hour episodes, with 2 Friends Entertainment acting as Executive Producers and US sales agent and Mainframe retaining international distribution rights.
In March 2010, Disney Channel aired a version of the story, Harriet the Spy: Blog Wars. This starred Wizards of Waverly Place cast member Jennifer Stone as Harriet, Alexander Conti from Cheaper by the Dozen 2 as Harriet's friend Sport, and Degrassi: The Next Generation's Melinda Shankar as Janie. In this film Harriet competes against Marion Hawthorne to see who has a better blog.